How are the radius report estimates calculated?
Great question. We're so glad you asked. First, a geographic information system (GIS) analysis calculates the project's radius(es). The GIS analysis then identifies the 2019 US Census Bureau block groups that intersect the project's radiuses. Then, the GIS analysis calculates the percent of each block group within each radius distance (overlap). Next, the overlap percent is multiplied by the demographics for each block group. Finally, the radius demographic estimate equals the sum of the overlap multiplied by the demographics for all block groups that intersect a radius.
The benefits of the methodology are that it allows for:
- the use of the most current data for small area geographies from the US Census Bureau;
- the estimation of demographics for radius distances using dissimilar shaped Census block groups; and
- data comparability (because estimates for small radiuses and large radiuses use the same methodology, geographies and data sets).
This methodology assumes that the population is equally distributed throughout a block group. This assumption can result in unlikely estimates for small radiuses (i.e. 1 mile) in rural areas with low population densities and thus, large geographic area block groups.