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Obtaining Map Data

Map data is available by the terabyte. Much of the existing map data is copyrighted material, which requires some form of release or compensation for use. Fortunately, the U.S. government has taken a liberal perspective on data compiled with tax dollars, releasing huge collections of map data to the public without copyright restriction, and at minimal cost. We will take advantage of this for our simple case study utilizing map data as well as demographic data from the U.S. Census Bureau. We will be looking at a county map of Massachusetts and then drilling down to a more detailed census tract map of a single county, Plymouth, MA. Census tracts are just one of several sets of boundary polygons for which the U.S. Census aggregates demographic data. This data, as well as data for any state in the U.S., is freely available from the Census Bureau Web site (http://www.census.gov).

Although this data is freely available, it will still need to be converted into the SVG format. At present, map data can be found in dozens of formats with generally widely published specifications. The standard Census Bureau format is TIGER, which stands for Topologically Integrated Geographic Encoded Reference. However, there are sources on the Census Web site for other well-known data formats. The data for this example has been converted to SVG format and made available for download from http://www.samspublishing.com.


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