Examining City GeoDemographic Drilldown; Intersecting Tracts and Places

.. how can “our city” do a better job of providing housing for low-income individuals and families? One part of a successful program involves looking at attributes of the neighborhood, or census tract, geography across the city. We need to analyze needs by city component census tracts, areas averaging 4,000 population. Here is how that might be approached — determining which census tracts. And while this applies to low income housing, it applies to many other planning topics.

Relate census tract geography to city/place geography using GIS tools for analytical purposes … determine which tracts intersect a city/place. This section considers intersecting tracts and places for illustrative purposes. But the methodology, and tools to do this, involve many, many other types of geography .. geographic spatial intersection. The inputs in this case are U.S. national scope 2020 census tracts (85,190 areas covering the U.S. wall-to-wall) and U.S. national scope 2020 places (32,188 areas). The output from the process of intersecting these geographies are tract-place intersecting parts (119,906 areas). There are 32,146 tracts that are wholly contained in places.

Developing Intersect Files
Tracts intersecting with cities can be determined using the VDAGIS Intersect tool. Select the two input shapefiles and name the intersect output shapefile. The intersect shapefile is added to the GIS project being used.

Focusing on a City
What tracts intersect a city of interest? By having this information, stakeholders, policymakers can study and better understand inequities, differences and needs across the city. Consider Santa Ana, CA (Orange County). There are 65 tracts that intersect with the city of Santa Ana. This could be any city across America. The following view shows Santa Ana with intersecting tracts.

By viewing the intersecting file in VDAGIS, intersecting tracts can be examined. The graphic below shows a zoom-in to tract 06059089102 (blue boundary). This tract is shown at the pointer in the above graphic. in the following zoom-in view, the white label shows the tract code for the whole tract and the two split parts are shown with the same code. The part to the right in Santa Ana city, the part to the left is in Garden Grove city.

Using the intersecting file, the list (a partial list) of these tracts and tract codes can be determined as shown below. By knowing the tract codes, detailed demographic-economic data can be pulled using DEDE and tract characteristics can be studied. Inequities ab be examined, special needs can be determined, east versus west tract groups might identify patterns to facilitate collaboration and policy development. What are the patterns of affordable housing across the city?

VDA Web GIS is a decision-making information resource designed to help stakeholders create and apply insight. Use VDA Web GIS with only a Web browser; nothing to install; GIS experience not required. VDA Web GIS has been developed and is maintained by Warren Glimpse, ProximityOne (Alexandria, VA) and Takashi Hamilton, Tsukasa Consulting (Osaka, Japan).

About the Author
Warren Glimpse is former senior Census Bureau statistician responsible for national scope statistical programs and innovative data access and use operations. He is also the former associate director of the U.S. Office of Federal Statistical Policy and Standards for data access and use. He has more than 20 years of experience in the private sector developing data resources and tools for integration and analysis of geographic, demographic, economic and business data. Join Warren on LinkedIn.

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