Census TIGER shapefiles – a primer
Earlier this year the Census Bureau released its TIGER/Line files in shapefile format for the first time. I was just taking a look at the TIGER website to see how the data would work as basemap for some simple projects we are working on. Keep in mind, I know there are other free and not so free data sources out there. This is just for those interested in using TIGER.
On first look, the structure of the files is significantly different from the original ASCII method. Those original file formats are arranged entirely by County. If you wanted more than just one county (like several adjoining counties for example), you had to merge the files through a program like TGR2SHP.
Now the shapefiles are arranged in a hierarchical structure that makes a little more sense and is potentially easier. The structure is based on National, State, and then County levels. For example, now if you want to use all TN counties combined into one shapefile, you can go to the Census TIGER shapefile webpage and select Tennessee. There you’ll see the full TN County shapefile. Or if you are looking for all of the zip codes across the country, you can now get a national shapefile of those in either 3-digit or 5-digit.
One primary difference with the new format is a file called All Lines. The All Lines shapefile includes linear features such as roads, railroads, and hydrography. One All Lines shapefile exists for each county or equivalent entity. Additional attribute data associated with the linear features found in the All Lines shapefiles are available in relationship files that you must also download but are located on the same page for convenience.
All in all, it looks like a good move if you are short on cash, don’t need super accurate data, and like the idea of using shapefiles. Here are a few quick links to get you started on documentation and such.
- TIGER/Line Shapefile FAQ’s
- CFCC to MTCFCC conversion document (Excel)
- TIGER/Line shapefile record layouts
- TIGER/Line shapefile relationships (ERD’s)
- TIGER/Line Shapefile web page
- TIGER/Line Shapefile FTP Site
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