Heatmap

A heatmap uses colour across a surface to show how a value varies from place to place. Unlike a choropleth, which shades administrative areas you already had, a heatmap divides the study area into a regular grid of its own and gives every cell a value.

In accessibility work the term means something more specific than a density picture. The value in each cell is a computed accessibility score: how far it is to the nearest supermarket, how many opportunities are reachable within fifteen minutes, how well connected the paths around it are. So the colour is a result, not a count of the input points, which is what a heatmap means in most other software. In GOAT the grid is the H3 hexagonal grid, and the scores come from routing calculations run from every cell.

That distinction matters when reading one. A heatmap of supermarket locations shows where the supermarkets are. A heatmap of supermarket accessibility shows where people can and cannot reach one, which is a different map and usually a more useful one.