Why are there so many different geographic level filter options?

#1

Why are there so many different geographic level filter options?

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#2

The NHGIS site now provides access to compound geographic levels, which represents a significant data expansion to the site. When you click to “show all geographic levels” on the Filter page, you see the standard geographic levels like Census Tract or County, but for each of these, there are numerous compound levels also available with labels describing exactly how the compound level is subdivided.

Standard geographic levels nest consistently within a hierarchy of larger units. For example, census tracts nest within counties, which in turn nest within states. This is a standard geographic level because census tracts cannot be split by county boundaries nor can counties be split by state boundaries. If you download data at this geographic level, a single record for each census tract is returned.

The non-standard or “compound” geographic levels consist of intersections between non-nesting standard levels. For example, you can now download census tracts in a State>Place>County hierarchy. Because census tracts do not nest within places, this geographic level will provide separate records for the portions of census tracts contained within different places, and a census tract’s code will appear in multiple records if multiple places fall within its boundary.

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