GAT Shapefile Preparation

Abigail Stamm

2023-03-15

Source: vignettes/gat_prepare_shapefile.Rmd

Shapefile specifications

This vignette provides the requirements for a shapefile that will be processed by the Geographic Aggregation Tool (GAT) and the necessary specifications if you wish to use GAT’s various options.

GAT requires an Esri shapefile. If your file is in another format, you will need to convert it to an Esri shapefile using R or your preferred GIS software.

Minimum requirements

The minimum requirements for your shapefile include:

  1. Polygon geometry: The layer shapes must be polygons, for example state outlines.
  2. Identifier variable: A character or string variable with unique values for each row.
  3. Aggregation variable: A numeric variable used for the aggregation.

These requirements allow you to merge areas using lowest count and closest geographic centroid merge settings.

Optional specifications

If you want to aggregate within a boundary, you will also need:

  1. Boundary variable: A character or string variable containing non-unique values.

If you want to use exclusion criteria, you will also need:

  1. Exclusion variables: Up to three numeric variables. If you have more than three exclusion variables or you need to exclude on character or string variables, create a numeric flag variable (for example 0, 1) to use instead.

If you want to merge on similar variables, you will also need:

  1. Numerator: A numeric variable to serve as the numerator in the ratio.
  2. Denominator: A numeric variable to serve as the denominator in the ratio. If you use the advanced setting limitdenom=TRUE, this variable cannot contain any zeroes after removing exclusions.

If you want to include a rate calculation (or ratio or density), you will also need:

  1. Numerator: A numeric variable to serve as the numerator in the ratio.
  2. Denominator: A numeric variable to serve as the denominator in the ratio. If you use the advanced setting limitdenom=TRUE, this variable cannot contain any zeroes after removing exclusions.

If you want to merge by the closest population-weighted centroid, you will also need another Esri shapefile, which can be the aggregation shapefile or an entirely different shapefile. It must include:

  1. Polygon geometry: The layer shapes must be polygons, for example state outlines.
  2. Population variable: A numeric variable used for the population counts.