Posts Tagged ‘zip code business patterns’

NYC Geodatabase Updates: Spatialite Upgrade & ZIPs to ZCTAs

Wednesday, July 30th, 2014

I released the latest version of the NYC geodatabase (nyc_gdb) a few weeks ago. In addition to simply updating the data (for subway stations and ridership, city point features, and ZIP Code Business Patterns data) I had to make a couple of serious upgrades.

Spatialite Updates

The first was that is was time for me to update the version of Spatialite I was using, from 2.4 to 4.1, and to update my documentation and tutorial from the Spatialite GUI 1.4 to 1.7. I used the spatialite_convert tool (see the bottom of this page for info)to upgrade and had no problem. There were some major benefits to making the switch. For one, writing statements that utilize spatial indexes is much simpler – this was version 2.4, generating a neighbor list of census tracts:

SELECT tract1.tractid AS tract, tract2.tractid AS neighbor
FROM a_tracts AS tract1, a_tracts AS tract2
WHERE ST_Touches(tract1.geometry, tract2.geometry) AND tract2.ROWID IN (
SELECT pkid FROM idx_a_tracts_geometry
WHERE pkid MATCH RTreeIntersects (MbrMinX(tract1.geometry), MbrMinY(tract1.geometry),
MbrMaxX(tract1.geometry), MbrMaxY(tract1.geometry)))

And here’s the same statement in 4.1 (for zctas instead of tracts):

SELECT zcta1.zcta AS zcta, zcta2.zcta AS neighbor
FROM a_zctas AS zcta1, a_zctas AS zcta2
WHERE ST_Touches(zcta1.geometry, zcta2.geometry)
AND zcta1.rowid IN (
SELECT rowid FROM SpatialIndex
WHERE f_table_name=’a_zctas’ AND search_frame=zcta2.geometry)
ORDER BY zcta, neighbor

There are also a number of improvements in the GUI. Tables generated by the user are now grouped under one heading for user data, and the internal tables are grouped under subsequent headings, so that users don’t have to sift through all the objects in the database to see what they need. The import options have improved – with shapefiles and dbfs you can now designate your own primary keys on import. You also have the option of importing Excel spreadsheets of the 97-2003 variety (.xls). In practice, if you want the import to go smoothly you have to designate data types (format-cells) in the Excel sheet (including number of decimal places) prior to importing.


I was hesitant to make the leap, because version 2.4 was the last version where they made pre-compiled binaries for all operating systems; after that, the only binaries are for MS Windows and for Mac and Linux you have to compile from source – which is daunting for many Mac users that I am ill-equipped to help. But now that Spatialite seems to be more fully integrated with QGIS (you can create databases with Q and using the DB Manager you can export layers to an existing database) I can always steer folks there as an alternative. As for Linux, more distros are including updated version of the GUI in their repositories which makes installation simple.

One of the latest features in Spatialite 4.1.1 is the ability to import XML ISO metadata into the database, where it’s stored as an XML-type blob in a dedicated table. Now that I’m doing more work with metadata this is something I’ll explore for the future.


The other big change was how the ZIP Code Business Patterns data is represented in the database. The ZBP data is reported for actual ZIP Codes that are taken from the addresses of the business establishments, while the boundaries in the nyc_gdb database are for ZIP Code Tabulation Areas (ZCTAs) from the Census. Previously, the ZBP data in the database only represented records for ZIP Codes that had a matching ZCTA number. As a result, ZIP Codes that lacked a corollary because they didn’t have any meaningful geographic area – the ZIP represented clusters of PO Boxes or large organizations that process a lot of mail – were omitted entirely.

In order to get a more accurate representation of business establishments in the City, I instituted a process to aggregate the ZIP Code data in the ZBP to the ZCTA level. I used the crosswalk table provided by the MCDC which assigns ZIPs to ZCTAs, so those PO Boxes and large institutions are assigned to the ZCTA where they are physically located. I used SQLite to import that crosswalk, imported the ZBP data, joined the two on the ZIP Code and did a group by on the ZCTA to sum employment, establishments, etc. For ZIPs that lacked data due to disclosure regulations, I added some note or flag columns that indicate how many businesses in a ZCTA are missing data. So now the data tables represent records for ZCTAs instead of ZIPs, and they can be joined to the ZCTA features and mapped.

The latest ZBP data in the new database is for 2012. I also went back and performed the same operation on the 2011 and 2010 ZBP data that was included in earlier databases, and have provided that data in CSV format for download in the archives page (in case anyone is using the old data and wants to go back and update it).

NYC Geodatabase in Spatialite

Wednesday, February 6th, 2013

I spent much of the fall semester and winter interim compiling and creating the NYC geodatabase (nyc_gdb), a desktop geodatabase resource for doing basic mapping and analysis at a neighborhood level – PUMAs, ZIP Codes / ZCTAs, and census tracts. There were several motivations for doing this. First and foremost, as someone who is constantly introducing new people to GIS it’s a pain sending people to a half dozen different websites to download shapefiles and process basic features and data before actually doing a project. By creating this resource I hoped to lower the hurdles a bit for newcomers; eventually they still need to learn about the original sources and data processing, but this gives them a chance to experiment and see the possibilities of GIS before getting into nitty gritty details.

Second, for people who are already familiar with GIS and who have various projects to work on (like me) this saves a lot of duplicated effort, as the db provides a foundation to build on and saves the trouble of starting from scratch each time.

Third, it gave me something new to learn and will allow me to build a second part to my open source GIS workshops. I finally sat down and hammered away with Spatialite (went through the Spatialite Cookbook from start to finish) and learned spatial SQL, so I could offer a resource that’s open source and will compliment my QGIS workshop. I was familiar with the Access personal geodatabases in ArcGIS, but for the most part these serve as simple containers. With the ability to run all the spatial SQL operations, Spatialite expands QGIS functionality, which was something I was really looking for.

My original hope was to create a server-based PostGIS database, but at this point I’m not set up to do that on my campus. I figured Spatialite was a good alternative – the basic operations and spatial SQL commands are relatively the same, and I figured I could eventually scale up to PostGIS when the time comes.

I also created an identical, MS Access version of the database for ArcGIS users. Once I got my features in Spatialite I exported them all out as shapefiles and imported them all via ArcCatalog – not too arduous as I don’t have a ton of features. I used the SQLite ODBC driver to import all of my data tables from SQLite into Access – that went flawlessly and was a real time saver; it just took a little bit of time to figure out how to set up (but this blog post helped).

The databases are focused on NYC features and resources, since that’s what my user base is primarily interested in. I purposefully used the Census TIGER files as the base, so that if people wanted to expand the features to the broader region they easily could. I spent a good deal of time creating generalized layers, so that users would have the primary water / coastline and large parks and wildlife areas as reference features for thematic maps, without having every single pond and patch of grass to clutter things up. I took several features (schools, subway stations, etc) from the City and the MTA that were stored in tables and converted them to point features so they’re readily useable.

Given that focus, it’s primarily of interest to NYC folks, but I figured it may be useful for others who wish to experiment with Spatialite. I assumed that most people who would be interested in the database would not be familiar with this format, so I wrote a tutorial that covers the database and it’s features, how to add and map data in QGIS, how to work with the data and do SQL / spatial SQL in the Spatialite GUI, and how to map data in ArcGIS using the Access Geodb. It’s Creative Commons, Attribution, Non-Commercial, Share-alike, so feel free to give it a try.

I spent a good amount of time building a process rather than just a product, so I’ll be able to update the db twice a year, as city features (schools, libraries, hospitals, transit) change and new census data (American Community Survey, ZIP Business Patterns) is released. Many of the Census features, as well as the 2010 Census data, will be static until 2020.

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