Find Component Geographies (Subgeography)

Overview

Component Geographies are boundaries selected within larger boundaries, for example, block groups inside a drive-time boundary.

Some examples include:

• Create an output feature class that includes all the ZIP Codes that intersect a drive-time trade area.
• Create a trade area of all the counties within a given state. In most cases, the correspondence between a parent and child geography is a strict hierarchical, one-to-many relationship.

Calculating Ratios

The Find Component Geographies tool gives you the option to calculate the statistical ratios of the underlying geographies. For example, you create component geographies of all ZIP Codes within a county. You can use the Calculate Ratios option to determine what percentage of ZIP Codes exists within the county boundary. Ratios for population, households, housing units, business counts, and general area can be generated. The ratio output appears in the trade area attribute table.

You can calculate ratios in the following ways:

• Area ratios only: This method means that a percentage will be calculated only where subgeographies intersect the boundary layer (for example, the percentage of area for each ZIP Code boundary within a county boundary).
• Area ratios plus population, housing units, and businesses: This method means that a percentage will be calculated only where component geographies intersect the boundary layer (for example, percentage of area for each ZIP Code boundary within a county boundary).

The attribute table containing ratios will look similar to the one below:

Tipp:

Component geographies can be created using these different selection methods:

• Interest
• Centroid Within
• Completely Within

Learn more about Find Component Geographies (Subgeography).