Append Data (Spatial Overlay)

Overview

The Append Data tool allows you to extract data from one layer, such as block groups, and add it to an overlay layer, such as a trade area that you have created in Business Analyst.

Spatial overlay allows you to answer questions such as How many households are there in my overlay polygons? What are the demographic characteristics of each of my customers? or What is the per capita income in this market area? Spatial overlay gives better answers to such questions than competing methods. The key idea is that data fields are assigned from an underlying data layer to an overlay layer.

Data Append in Business Analyst has been improved to work not only with polygons but also with point layers. The possible input layer and overlay layer combinations are the following:

Input layer|Overlay layer

Polygon→Polygon

Point→Polygon

Polygon→Point

Example output

If the overlay layer is a polygon and cuts across a polygon input layer, the data will be apportioned based on the apportionment method identified in the Custom Data Setup wizard. This will be one of the four method choices: area, population (block point), households (block point), or total housing units (block point). Geography layers that come with Business Analyst are already set up but can be changed using the Analysis Layer Setup wizard.

Begin with a simple example of area apportionment of population. If a block group falls totally within the overlay polygon, all its population is counted. If only 45 percent of the block group falls within the overlay polygon, only 45 percent of its population is counted. This gives you a more accurate estimate than if you just added up the polygons that touched or had their center within the overlay polygon.

Apportioning, based on block point data (population, households, or housing units) is a better method than area apportionment. A majority of a block group's population may reside in one quadrant of the block group. Apportioning by area doesn't take this into account.

To illustrate how different area and block apportionment can capture data, examine the following example. In the image below, the black points represent the block point locations, the bright yellow boundary is a drive-time trade area, and Census geographies are represented by the black boundaries. As you can see, 81 percent of the block points in the Census geography are captured in the drive-time trade area using a block centroid approach, but only 45 percent of the data would be captured if you were using an area approach. The block apportionment is considerably more accurate in this example.

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Limit your number of variables to append to less than 1024 or you may experience issues displaying the data.

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You can run Data Append on any Business Analyst data source (BDS) loaded into your table of contents or from our online servers.

Learn more about Append Data (Spatial Overlay).