Calculating Trade Area Demographics

Demographic data is stored at the block level which is a geographic area defined by the US Census Bureau. To roll this data up to the trade area from the block group we apply one of two methodologies based on the metric. For metrics that are summed we use methodology 1. For metrics that are averages or medians we use methodology 2.

Metrics using methodology 1

Metrics using methodology 2

Using the examples above, you can see that population (households) are concentrated to certain areas in the Radius. When the block groups are turned on, the outer block groups touches both the outside and inside of the 3 mile radius. We do not assume population is evenly spread across a census block group. Instead, we use the actual concentration of households within the block group. When measuring population inside a radius, only the population that lives inside the overlapping portion is counted—not a simple area-weighted average of the entire block group.

Using the same example above. We do not assume households are evenly distributed across a census block group. When calculating median household income within a radius, we use only the households that actually fall inside the selected area, rather than prorating the entire block group’s median income by land area.

Note: There is no difference in how our trade area data is calculated between US Census and EASI as both sources provide data at the block group level.