Putting transit GIS data to use


I was reminded recently that Albert Sun‘s terrific Wall St Journal interactive about the spatial patterns of Metrocard usage uses the subway routes in GIS format that I created.  It’s not a major part of the map; the routes are used as a backdrop more than anything. But I was glad the Journal was able to use the data.  (Per the notes from the map, the subway data was “from the MTA. Demographic data from the U.S. Census Bureau. Additional work refining subway line shapes from the CUNY Mapping Service at the City University of NY Graduate Center.”)  Here’s a screen shot:


Recently I’ve come across several examples of people being able to use the MTA subway and bus data that I had converted to GIS format a couple of years ago.  I know that I’ve been able to put the data to good use.  But I’m especially glad to see others benefiting from my efforts.

So I thought I’d share some maps and links below.  Hopefully this will inspire others to use the data, and to let us know about other examples.  If you’ve been able to use the subway or bus GIS data, please let drop me a line by email or add a comment to this post.  Thanks!

Distance Cartograms

Zach Nichols wrote a week ago that he incorporated my GIS version of NYC subway routes into a blog post about “re-scaling NYC based on MTA transit time.”  Here’s one of his maps (a “distance cartogram”); very cool!

Mobile apps

One of the entrants in last year’s MTA AppQuest contest used the subway route GIS data as a layer on their map for reference.  The app — Dead Escalators — is being updated for distribution in the iTunes App Store.  Look for it there soon!  In the meantime, here are a couple of screen shots:


GIS data for student projects

  1. Liz Barry’s students at the New School are incorporating the data into their projects.  Glad to be of help, and thanks Liz for your kind words!
  2. Christopher Bride, a GIS student at CUNY’s Lehman College, used the data for his Capstone project this year examining the intersection of food deserts and the likely route home from subway/bus stations.  The project’s goal is to pinpoint fresh food-critical neighborhoods in New York City.  Here are two sample maps, focused on the Bronx:

  1. Lauren Singleton-Meyers at NYU’s Steinhardt School of Culture, Education and Human Development used the subway routes for a project with the New York Center for Alcohol Policy Solutions, for a campaign she’s launched to stop alcohol advertising on public transportation in the city.  As a start, she’s mapped schools and subway routes and stations.  Next steps will be to link pictures of alcohol ads to the subway route lines as part of an educational effort showing what types of ads are being displayed on each route.

Here’s her map (a work in progress) via ArcGISOnline and ArcGIS Explorer:

  Here are some example photos via her Flickr stream.  If anyone has suggestions on helping her with the next steps for her map, please get in touch (their Twitter handle is @EMTAA).

Inspiring similar efforts in other cities

Soon after I wrote my blog post with the MTA’s data in GIS format, it had an impact not only here in New York but in at least one other city: Chicago.  Blogger and urban planning advocate Steve Vance adapted my methodology to transform the GTFS data from the Chicago Transit Authority into GIS format.  Here’s his post: http://www.stevencanplan.com/2010/obtaining-chicago-transit-authority-geodata/ , plus a more in-depth discussion of his technique: http://www.stevencanplan.com/2010/how-to-convert-gtfs-to-shapefiles-and-kml/

Proximity of bus stops to pedestrian accidents

This week the Tri-State Transportation Campaign published an analysis of pedestrian fatalities in Nassau County and several towns in Connecticut, and noted that in Nassau, for example, 83% of the fatalities from 2008-2010 occurred within a quarter-mile of a bus stop.  The group used my GIS version of MTA’s bus GTFS data for their analysis.

I haven’t examined TSTC’s report closely, so I’m not sure how strong of a causal relationship exists between bus stops, per se, and the fatalities (an anonymous commenter at TSTC’s blog argues that “Of course the most pedestrian deaths occur near bus stops, they’re located in the only places in the county where anyone actually walks”).

But one observer on Twitter, @capntransit, wondered if buses are so ubiquitous that the relationship would be a non-issue (they wrote “Isn’t 85% of Nassau County within a quarter-mile of a bus stop?”)  I thought I’d try to answer, and came up with the following by mapping the bus stops and block-level population data from the 2010 Census:

  • Nassau County’s land area is 285 square miles.  The area within 1/4 mile of all LI Bus stops is 119 square miles (42% of the county area); and
  • Nassau’s population in 2010 was 1.34 million people.  The population within 1/4 mile of all LI Bus stops in 2010 was 838,524 people (63% of the county population).
  • So on the face of it, the concentration of fatalities near bus stops seems disproportionately higher than the overall nearby population.  The map below highlights the bus stop coverage:

I’m glad my data conversion efforts have been helpful.  It’s only possible due to the MTA’s ongoing effort to provide easy public access to their data sets.  This enables me and many others to help improve life in and around the city by integrating their data into maps, applications, government accountability efforts, and more.  Please send more examples of how you’ve been able to use the data; highlighting these projects helps us all.

Proposed Congressional districts for NYS available in GIS format

UPDATE June 25, 2012

We launched a companion map featuring Congressional districts with statistics on eligible voters by race/ethnicity compared with total population.

UPDATE March 6, 2012

We’ve added Congressional districts as proposed by District Court Judge Hon. Roanne Mann to our interactive redistricting site. Here’s a link that compares District 9 (Rep. Turner, in NYC) with one of the proposed districts that it would become under her proposed lines: http://t.co/01K4hMu8

We also submitted a letter today to the court [PDF] suggesting that they can use our maps to visually compare the different proposed lines.  Hopefully they’ll put our online maps to good use as they review the different Congressional district proposals.

UPDATE March 5, 2012

We’ve made two updates the information below.

  1. We’ve added the Congressional district data in shapefile and KMZ formats based on Common Cause’s submission to the court.  We think this will be especially helpful since the court has asked the intervenors to compare their maps with Common Cause’s proposal.
  2. Now you can visualize the proposed districts based on the mapped data below at the Center for Urban Research’s interactive redistricting site.
    1. compare with existing Congressional districts;
    2. easily switch among the Congressional proposals from Common Cause and the Senate & Assembly majorities; and
    3. view the proposed districts in relation to block-level demographic maps (do any of them appear to “pack,” “crack,” or dilute the potential voting power of minority populations?) or local voting patterns (click the “More Data” tab at the bottom right).

Here are some examples:

Today the New York World posted an analysis of how these different Congressional district proposals might impact Rep. Charles Rangel’s current district 15.

Original Post

If you’re hoping to use GIS or any of the online mapping tools to map the Congressional district lines in New York State that were proposed late yesterday, you’ll have some work to do.  The maps were released in PDF format as well as “block assignment lists” for the proposed districts.

But if you’d like to use shapefiles and/or KML files, you’ve come to right place!  Our team at the CUNY Graduate Center has created them and posted them for downloading here:


We hope to add these soon to our interactive redistricting map. Stay tuned!

NYC’s open data legislation: reading between the lines

TL; DR (i.e., the summary)

NYC is about to adopt what some are calling “landmark” and “historic” legislation regarding open data.  Does the hype match the reality?

I offer the analysis below not as a critique of the City Council.  I think they probably tried to negotiate as good a bill as they thought they could achieve.  I offer it more as food for thought for those of us who will be seeking the data that may eventually become available because of the legislation (and for those of us who rely on data that’s currently available that may become less so due to the bill).

Hopefully my concerns represent a worst case scenario.  If the bill’s implementation indeed lives up to the “landmark” status bestowed on its passage, that would be a great thing.

For example, the Council’s committee report on the bill [Word doc] suggested that substantial city data sets such as the Building Information System (BIS) or the Automated City Register Information System (ACRIS) would be made available in open, accessible formats due to the legislation. If that happens, that would be great.  But for each of the handful of examples like that suggested at yesterday’s Council committee meeting, I could offer several more that I believe might escape the requirements of this bill.

My overall sense is that somewhere during the two-plus years the bill has been on the table, the details got in the way of the original vision embodied in this proposal.  And, as they say, the devil is in the details.  If you’re interested in my take on those gory details, please read on.

An important step

The bill is important, in a way. It’s an acknowledgment by the City Council (and the Mayor, if he signs it) that city agencies need to provide public access to data sets online, in a standardized electronic format.

In doing so, it goes a step beyond FOIL — the New York State law since the mid-1970s that has required agencies (including local government) to provide public access to data.  Though FOIL has adapted to the times to some extent — the courts and policymakers now understand that FOIL applies to electronic data as well as printed material — it is still a reactive approach.  You have to submit a FOIL request (and have a good idea of what data you’re requesting) for an agency to respond and give you access.  New York’s Committee on Open Government describes it as “pull” vs. “push”. [PDF]

Some smart agencies have realized that posting data electronically saves money, time, and effort. By posting data online proactively, before the agency even receives a single FOIL letter  (“pushing” it so people don’t have to “pull” it), it avoids having to respond individually to FOIL requests.

So the City Council bill acknowledges that pushing is better than pulling.

Those devilish details

But will the legislation require agencies to post data online?  To some extent, yes.  But how far that goes depends on how it’s interpreted, and how aggressively it’s implemented (and perhaps how strongly the public reacts, since it seems like the only enforcement mechanism is public reaction).

The first substantive part of the bill says that within a year, agencies need to post their data at the city’s online data portal.  But let’s look closely at the language.  Section 23-502(a) says that within a year, agencies don’t need to publish all their data to the portal.  Only “the public data sets that agencies make available on the Internet” need to be included in the portal (emphasis mine).

In other words, if an agency has refused to provide public access to a data set, or perhaps only allows access to that data after you’ve paid a fee and/or signed a license agreement, or otherwise hasn’t already posted the data online — that data is exempt.

Then it gives agencies another loophole.  The next sentence says that even if an agency has a data set online, it doesn’t need to post it on the portal if they “cannot” put it on the portal.  (“Cannot” isn’t defined in the bill.  Does it mean “doesn’t want to”? Does it mean the data’s too complex for some reason?  “Cannot” seems to offer quite a bit of wiggle room.)

The bill further states:

the agency shall report to the department and to the council which public data set or sets that it is unable to make available, the reasons why it cannot do so and the date by which the agency expects that such public data set or sets will be available on the single web portal.

I’m not a lawyer, but it seems to me that if an agency doesn’t want to comply, it just needs to give a reason.  And it needs to give a date by when it will add the data to the portal.  The date could be two years from now, or it could be two decades from now.  That part of the bill doesn’t have a deadline.

Without aggressive support from the top — the Mayor and/or perhaps a new Chief Data Officer position with some teeth — agencies could just take their ball and go home and not play the open data game.  And the public will be the worse for it without much recourse.

Over-reliance on “the portal”

Let’s be optimistic and assume that all city agencies (even the current holdouts – I’m looking at you, City Planning Department & MapPLUTO) decide to post their data online.

The bill doesn’t say, or even mention as an option, that agencies can keep posting the data online at their own websites.  Instead, it has to be posted on “a single web portal that is linked to nyc.gov”.

But I’m not as enthusiastic as I once was for the portal approach (currently implemented here).

  1. Data for APIs, or people?

At first I thought the portal would be so much better than the city’s earlier Datamine site. But the site seems to focus heavily on APIs and web service access to the data, which might be great for programmers and app developers, but not so good for people, like Community Board staff, or reporters, or students, or anyone else who just wants to download the data and work with the files themselves.

  1. Some agency websites are doing a better job

Also, why not allow — even encourage — agencies to continue posting data on their own websites?  I think that, in many instances, the individual agencies are doing a better job than the data portal. The files available for downloading from agency sites such as Finance, City Planning, Buildings, and Health are more up to date, more comprehensive (though still hardly complete), and easier to understand than what I can find on the portal.

I think it would be ok if both approaches existed (portal and individual agency sites). But the way the bill is worded, I think the risk is that agencies are more likely to do only what they have to do or what they’re expected to do.  Since the bill focuses on the portal, I think we may see individual agency data sites whither away, the rationale being why bother with individual sites since they have to post to the portal.  With sites such as City Planning’s Bytes of the Big Apple (which is really great, with the exception of the PLUTO license/fee), I think that could be a big loss for the many people and organizations who have come to rely on the high quality data access that these agency sites provide.  Hopefully I’ll be proven wrong.

  1. The current portal falls far short of a forum for public discussion

The bill requires DoITT to

implement an on-line forum to solicit feedback from the public and to encourage public discussion on open data policies and public data set availability on the web portal.

But if the current portal is the model for this online forum, I’m concerned.

When I access data from the agencies themselves, I can talk with the people directly responsible for creating and maintaining the data I’m seeking. I can have conversations with them to understand the data’s limitations. I can discuss with them how I’m planning to use the data, and if they think my expectations of the data are realistic.

In contrast, the portal requires me to either go through a web form (which I’ve done, and received zero communication in return), or to contact someone who has no identification beyond their name (or some online handle).  Do they work for an agency?  Do they even work for New York City?  I have no idea; the portal provides no information.  So much for a site that’s supposed to be promoting “transparency in government.”

To me, the portal is somewhat analogous to the city’s 311 system and the recent articles about putting the city’s Green Book online.  Though 311 is great in a lot of ways, it has put a wall between the public and individual city agency staff members.  Try finding a specific staffperson’s contact information via nyc.gov, like the New York Times recently did.  It’s almost impossible; you have to communicate through 311. Similarly, the online data portal — if it ends up replacing agency websites as sources for online data access — will make it difficult to locate someone knowledgeable about the data.

This widens the “data gap” — the gap of knowledge between data creators and data users.  In order to know whether a particular data set meets my needs (if I’m creating an app, or even just writing a term paper), sometimes a written description of the data is not enough.  I may need to actually talk with someone about the data set.

But good luck finding that person through the data portal.

And even when people have used the portal to submit online comments, I don’t know if anything ever comes of it.  It looks like only 14 of the 800+ datasets at the portal have comments (sort the list by “Most Comments”).  All of the comments raise important questions about the data.  For example, two people offered comments about the HPD Registration data available through the portal.  They asked “Is there any plan to expand it?” and “Could you help us?”  Both remain unanswered.

Maybe everyone who commented was contacted “offline”, as they say.  Either way, this hardly constitutes a forum for public discussion.  No public interactivity.  No transparency.  No guidance.  It’s no wonder there’s been so little use of the portal’s  button (and I use the term “Discuss” loosely).

Public data inventory

Another section of the bill has a nugget of hope.  But the way it’s worded, I’m not too optimistic.

Section 23-506(a) says that within 18 months, DoITT shall present a “compliance plan” to the Mayor, the Council, and the public.  Among other things, the plan must “include a summary description of public data sets under the control of each agency.”

In effect, this “summary description” (if it’s done right) will be the public data inventory that advocates have been pushing for (and which has been required by the NYC Charter since 1989). That’s a good thing. At least now we’ll know what data sets each agency maintains.

Hopefully it’ll be a comprehensive list. I guess the list’s comprehensiveness will be up to DoITT to enforce. (And if the list comes up obviously short, perhaps some enterprising FOILers can point out — very publicly — where the holes are ;) ).

But that same section of the bill also says that the plan “shall prioritize such public data sets for inclusion on the single web portal on or before December 31, 2018“.  So it still relies solely on the data portal. And it gives the city another 6 years to make the data public. As someone said on Twitter, “sheesh”!

Then there’s another loophole.  The bill allows agencies to avoid meeting even the 2018 deadline by allowing them to

state the reasons why such [public data] set or sets cannot be made available, and, to the extent practicable, the date by which the agency that owns the data believes that it will be available on the single web portal.

“[T]o the extent practicable”?  When the agency “believes” it’ll be available?  Wow.  Those are some loose terms.  If I ran an agency and didn’t want to provide online access to my department’s data, I’d probably feel pretty confident I could continue preventing public access while easily complying with the law.

Where does this all leave us?

It looks like the City Council will pass this law, despite its limitations.  In fact, DoITT was so confident the law will pass, it emailed its February 2012 newsletter on the day the Council’s technology committee voted on the bill (Feb. 28, a day ahead of the expected full Council vote).  Here’s what the newsletter said about Intro 29-A:

“Will be voted on and then passed”?  I guess the full Council vote is pretty much a foregone conclusion.

That leaves us to hope that the bill’s implementation will address the issues I’ve outlined above, and any others that advocates may have identified.  Fingers crossed?

(Disclaimer: my viewpoints on this blog are my own, not necessarily my employer’s.)

Redistricting’s partisan impacts: a GIS analysis

Our team at the Center for Urban Research is collaborating with The New York World to analyze the impacts of redistricting in New York State.  The latest effort was featured today on the front page of the Times Union; it focuses on how the majority parties in the State Senate and Assembly would likely retain — and strengthen — their control of both houses through the redrawn district lines.

Briefly, we found that the new boundaries for state Senate and Assembly districts proposed by LATFOR would increase the number of seats held by the majority parties in both chambers.  We based the analysis on 2010 election data available from LATFOR’s website.  The goal was to determine the results of state legislative elections held within the new districts if voters cast their ballots in the exact same way as they did in 2010, the most recent election year for State Senate and Assembly.

  • In the State Senate, the Republican Party’s 32-to-30 majority would expand to 34-to-29 if each voter cast his or her ballot in support of the same party as in the 2010 elections.
  • In the State Assembly, the 98-to-50 advantage the Democrats enjoyed following 2010’s elections would also increase, to 102-to-48.

The project was a good example of the power of GIS.  The analysis didn’t necessarily need a map to display the results (though Michael Keller at the NY World put together a nice one). But the analysis effectively wouldn’t have been possible without GIS.

Converting Polygons to Points

We analyzed election results at the level of voter tabulation districts, or VTDs, which are several blocks in size and typically cast no more than a few hundred votes in state legislative elections.  We mapped the VTDs onto the new lines proposed by LATFOR, then added up the votes of all VTDs that fell within a proposed district to determine its outcome.

In order to allocate the VTD-level vote counts to LATFOR’s proposed districts, CUR matched VTDs spatially with the current and proposed legislative district using ESRI’s ArcGIS Desktop software. The current and proposed Senate and Assembly districts are coterminous with Census blocks (in fact, the districts are “built” using Census blocks).  Unfortunately, neither LATFOR nor the state’s Board of Elections provides election results at the block level.  The Board of Elections records data by election district, which sometimes are smaller than VTDs, but for this project we did not have access to the election district data.

The challenge was that where the VTDs were larger than Census blocks in some places, the VTD boundaries crisscrossed the district lines (see example at right from Queens; click to enlarge).  In order to assign Senate and Assembly district IDs to each VTD, CUR converted the VTD boundaries to centroids (the geographic center-point of each VTD).  We used the lat/lon centroid values provided by the Census Bureau’s TIGER data.  Then we used a spatial join using ArcGIS to add legislative district identifiers to each VTD based on the legislative district its centroid was inside.  See the image below for the locations of the VTD centroids in this area of Queens.

In the instances where VTDs crisscross legislative districts, this technique will allocate all of a VTD’s votes to a single legislative district rather than splitting them across multiple districts.  This will over- and underestimate vote totals in some districts. But the process avoids the cumbersome effort involved in the alternative: splitting VTD vote counts.  The splitting process uses one of two methods:

  • using block-level population to “spread” the VTD votes across the VTD (multiplying the VTD vote count by the percentage of the VTD population occupied by each block and assigning the result to each block), or
  • weighting the VTD vote count based on the area of the portion of the VTD in each district.

Either of these approaches will result in fractions of people being assigned to one legislative district or another.  In fact, LATFOR appears to have used some sort of weighting method to assign election district vote counts to VTDs, since some of LATFOR’s VTD vote totals included fractions.

The centroid-approach and the weighted population / area approach both make assumptions about how to allocate vote counts.  But we tested the centroid process with current legislative districts and found that our VTD-allocated vote totals either exactly matched the results from the Board of Elections or were within a few hundred votes (which did not change the 2010 outcome).

Whether we used the centroid-approach and the weighted population / area technique, it otherwise would’ve been difficult if not impossible to determine how to allocate the VTD-level vote counts to legislative districts without GIS.  There are almost 15,000 VTDs across New York State, and there are (currently) 62 Senate districts and 150 Assembly districts.  With GIS, the process was relatively straightforward and efficient.

Aggregating by District

At the VTD-level, LATFOR provides the total number of votes cast by party in each election, not by candidate.  One challenge that we confronted was assigning the votes cast for fusion candidates who were backed by a major party but also received support on smaller parties’ ballot lines.  For example, many Democratic candidates received significant numbers of votes on the Working Families Party ballot line, and many Republicans got substantial support on the Conservative Party line.  Cross-party endorsements were even more variable for the Independence Party: in some districts, the Democrat received support on the Independence Party line; in others, its endorsement went to the Republican.

We decided that the most accurate way to re-map the election results was to assign the votes for each VTD based on the actual vote patterns for the Senate or Assembly district that contained that VTD in 2010.  In other words, if the Democratic candidate in an Assembly district ran on the Democratic, Conservative, and Independence lines, we assigned the Democratic, Conservative, and Independence votes in all the VTDs in that district to the Democratic candidate.  When we allocated the VTDs to the proposed Senate and Assembly districts, we added up the votes based on these patterns.  This ensured that the local voting patterns from 2010 were allocated accurately to the proposed districts.

The Results: Maps vs. Plain Old Numbers

The result is that we were able to calculate the number of proposed districts that, all other things being equal, would have had a Democratic winner in the Assembly and a Republican winner in the State Senate.  The important finding is that both parties would have increased their majority — which is especially interesting in the Senate, where the Republicans currently only have a 1-seat majority.  In Albany, the majority in each house is extremely powerful, so holding on to (or improving) those margins is all-important.

Of course, as the New York World/Times Union article points out,

To be sure, no district votes the exactly the same way in consecutive elections: the quality of candidates, changes in the population and the national political climate (which in 2010 favored Republicans) all play important roles. But voting behavior in previous elections offers the best available indication as to how a district is likely to perform.

The map that the New York World published along with the article uses red/blue color-shading to visualize the impact of the voting patterns on the proposed districts.  In the state Senate, the analysis shows the majority party increasing the number of seats by two.  On the map, that result is almost lost in the sea of red districts (most of the Republican seats are in upstate New York and Long Island, where the districts cover much larger areas than the more densely populated and largely Democratic districts in New York City).  The real power of our finding is the change in number: from 32 to 34.  In some ways, that says it all.

Nonetheless, the map (along with CUR’s interactive map comparing current and proposed district boundaries) provides a strong graphic and interactive element to the story, and provides context as you move your mouse over the districts to see the vote totals change from one to the next.

Watch for more analysis as LATFOR publishes its proposed Congressional district lines, and when the final Senate and Assembly districts are drawn.

Interactive NY redistricting map with cartoDB and more

UPDATE Nov. 5, 2012

In preparation for the Nov. 2012 election, many news organizations and others are linking to our interactive State Legislature and Congressional redistricting maps. We’ve posted examples at the Center for Urban Research website.

UPDATE Sept. 7, 2012

We’ve updated our map of redistricted State Senate and Assembly districts, highlighting the differences in race/ethnicity characteristics between total population and voter-eligible population – in other words, comparing the characteristics of all those who live in the new districts versus the smaller group who will be eligible to vote for each district’s representatives.  In some cases the differences are striking.

Our examination of the district-by-district data is available here.

New York State, like all other states, is in the midst of redrawing its legislative district lines. To help you follow along, our team at the Center for Urban Research has launched an interactive redistricting map for New York.  We collaborated with The New York World to develop the maps (though we encourage anyone and everyone to use them!).

The World’s reporters and editors are using our maps to go between the lines and explain how redistricting really works in the Empire State. (Here’s their first piece: The art of redistricting war.)  And we hope you’ll be able to use the maps too, to help answer questions such as:

  • Will you still be represented by the same State Senate or Assembly district you live in now?
  • Will you live in the newly proposed (and controversial) 63rd Senate district?
  • Is your neighborhood, town, or county going to be “carved up” by a new legislative seat?
  • Will your community’s historical voting power be diluted by the new districts?

We have some examples of gerrymandering at our Center’s website. In the meantime, here’s how you can use the maps.

Map features

The maps compare the current and proposed district lines (which our team mapped based on Census block lists published by the state’s redistricting task force, known as LATFOR). Here’s how they work:

  • Enter your address to find out what district currently represents you, and which proposed district you’d live in.
  • The current districts are on the left, and the proposed districts on the right.
  • You can also click on either map to highlight the current and proposed districts. As you move one map, the other moves in sync.
  • When you enter an address or click on the map, an info window pops up listing the current and proposed districts. You can click the link for the current district to go to that Senator or Assemblymember’s website.
  • Switch between State Senate and Assembly districts. Congressional districts will be posted once the data is available from LATFOR.
  • You can zoom in to street level, or zoom out to a statewide view. Switch between a street basemap or an aerial view from Microsoft’s Bing maps to see geographic details.

If you’re using the “Overlay” view, you can move the transparency slider to the right to display proposed districts, and to the left to fade back to current districts. The video below shows how:

If you want to share the map you’ve made, click the “Link” in the upper right of the map page to get a direct link to the area of the map you’re viewing. It will look like this:

  • You can share this on Twitter, Facebook, etc and email it to friends and colleagues.
  • You can also embed the map at your site. Use this link …
  • … or add < &output=embed > to any of the direct links you create, like this:
  • … or wrap the snippet below in an iframe tag (I’d wrap it myself, but wordpress.com strips out iframe tags):
frameborder="0" marginwidth="0" marginheight="0" 
scrolling="no" width="600" height="700"

Side-by-side maps with OpenLayers

We borrowed from our “Census Comparinator” mapping site that Dave Burgoon artfully developed, in order to provide three ways to compare the current and proposed legislative districts:

  • a side-by-side view — two maps that are synced and move as one;
  • an overlay — a single map where you can fade between current and proposed districts; and
  • the vertical “before-and-after” slider approach.

I blogged about the Comparinator approach here and here. John Reiser also gave the technique a shoutout at his “Learning Web Mapping” blog for Rowan University.

With Census data, our “Comparinator” approach helped visualize changing spatial patterns of race/ethnicity trends – in cartographic terms, between two choropleth maps. With legislative districts, the comparison is between two sets of boundary files with no inner fill. So here we’ve set the side-by-side view as the default — we think the side by side maps give the easiest way of visualizing how the districts may change. But we also give you the option of viewing the districts with our vertical slider bar if you’d like, or the overlay.

Behind the scenes

For the proposed districts, we used ArcGIS to create the legislative district shapefiles based on LATFOR’s Census block assignment lists.  The current district boundaries are from the Census Bureau’s TIGER files (here’s the FTP page if you’d like to download the “lower” house districts — in New York, that’s the Assembly — or the “upper” house shapefiles — the State Senate).

We use OpenLayers for the map display and navigation with this application, as we’ve done with most of our other interactive maps. OpenLayers is easy to use, enables us to access Bing map tiles directly (so the basemap performance is smooth), and provides a robust JavaScript library for online maps.

That said, newer approaches such as Leaflet.js enable more interaction such as mouseovers, so we’ve started experimenting with some impressive new tools. More to follow!

One of those new tools is the powerful backend geospatial database engine from the team at Vizzuality: cartoDB. Hosting the legislative district shapefiles on cartoDB provided lots of advantages over hosting the data ourselves or setting up an Amazon cloud instance on our own. cartoDB provides:

  • great performance — not only for the district boundaries, but soon we’ll be adding election district maps to show voting patterns within each Senate and Assembly district. We don’t want to bother with creating pre-rendered tiles for this data. cartoDB will render it speedily on the fly.
  • cartographic flexibility: cartoDB uses cartoCSS for map symbology and labeling. Though there are still some quirks with cartoCSS, it was easy to grasp and it’s basically just CSS, so it makes styling easy if you’re familiar with modern web design. And cartoCSS incorporates scale-dependent rendering as well as attribute-based symbology, which makes it powerful and flexible. CartoCSS can be implemented using the cartoDB management interface, or programmatically.
  • easy data management: if you know SQL — and even better, if you’re familiar with SQL commands with PostGIS — you can quickly and easily modify tables, filter data, and perform spatial operations. (The screenshots at the cartoDB github page offer some examples.) Very cool.
  • scaling: cartoDB uses PostGIS and makes use of Amazon’s platform. So if our maps go viral, we’re ready for the usage spike!
  • open source: if you want to manage your own instance of cartoDB, just download the code and go! Big props to Vizzuality for an amazing geospatial toolkit.

Other thanks go to:

  • LATFOR, the state’s redistricting task force. Whatever you think about their redistricting process, they’ve done a great job with open data. They’ve not only posted the list of Census blocks that make up each proposed legislative district. But they also posted a wealth of data at the Census block level and also at the election district level (with a crosswalk between EDs and Census “voter tabulation districts”). This data is indispensable for visualizing, analyzing, and (hopefully) making sense of the new districts.
  • Dave Burgoon and the CUR team. Dave put together the redistricting mapping site in record time. Although it’s based on work he had already done with the Census Comparinator maps, it still involved substantial modifications and enhancements. But he made it happen as professionally and elegantly as always.
  • The New York World. We had been planning to create an interactive mapping application to build on our Census Comparinator site and to help people visualize the impacts of the redistricting process and demographic changes more broadly.  But the World team – Alyssa Katz, Michael Keller, and Sasha Chavkin – met with us a few weeks ago to discuss how we could collaborate on analyzing and mapping the upcoming district proposals from LATFOR.  The discussion inspired us to roll out a mapping site specific to New York State and focused on comparing the current and proposed districts. We’re thrilled to be able to work closely with them on this project (watch for more maps and data in the near future!).
  • The Hagedorn Foundation. The Foundation has provided funding support for our efforts to map and analyze Census data for a variety of civic engagement purposes, especially for Hagedorn’s Long Island-based grantees but also nationwide. Their support has been essential for us to develop innovative mapping applications like the NYS redistricting maps – not to advocate specific district plans one way or another, but to give local residents and others the tools they need to understand the impact of redistricting and hopefully get involved in the process.

Proposed NYS Senate & Assembly districts available in GIS format

UPDATE Nov. 5, 2012

In preparation for the Nov. 2012 election, many news organizations and others are linking to our interactive State Legislature and Congressional redistricting maps. We’ve posted examples at the Center for Urban Research website.

UPDATE Sept. 7, 2012

We’ve updated our map of redistricted State Senate and Assembly districts, highlighting the differences in race/ethnicity characteristics between total population and voter-eligible population – in other words, comparing the characteristics of all those who live in the new districts versus the smaller group who will be eligible to vote for each district’s representatives.  In some cases the differences are striking.

Our examination of the district-by-district data is available here.  The New York Times gave our analysis a shout-out in their CityRoom primary election day column.

You can also visit our original NYS redistricting “comparinator” map described below, at www.urbanresearchmaps.org/nyredistricting/map.html

UPDATE February 5, 2012

You can visualize these proposed districts in relation to the current New York State Senate and Assembly districts with our new interactive redistricting map.  We developed the interactive map in collaboration with The New York World, and here’s an article using the maps to describe the redistricting process in the Empire State.  For more background on the interactive map, visit this blog post.

Original Post

If you’re hoping to use GIS or any of the online mapping tools to map the legislative district lines in New York State that were proposed today by the state’s redistricting task force, you’ll have some work to do.  The Task Force released PDF maps as well as “block assignment lists” for the proposed districts.

Unless you’d like to use the shapefiles and/or KML files that our team at the CUNY Graduate Center created!  Here’s our web page with the info: http://www.urbanresearch.org/news/proposed-nys-districts-in-gis-format

Happy redistricting mapping!

Access to local GIS data

Rob Goodspeed has an interesting post about his survey of the policies and practices of local governments in Massachusetts regarding GIS data. It looks like a good read. In my experience (in New York State), local governments can have more interesting GIS data (for example, tax parcels and real property records) than the state or Feds, but their data access policies and/or practices can be more limiting. There are major exceptions (NYC, for example), but even New York City requires a fee and restrictive license to access its property data.

I look forward to reading Rob’s paper. Among other things, Rob is a PhD student at MIT. Nick Grossman of Civic Commons first alerted me to the paper via Twitter.


Get every new post delivered to your Inbox.

Join 1,540 other followers