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Heat map

A heat map shows concentration or intensity using color. Learn why its appearance depends on radius, scale, weights, and the records included.

A heat map uses color to show the concentration or intensity of values. On a public-safety map, it often turns many incident points into a smooth display of relatively denser and sparser areas. Its appearance depends on the data and display method, not just on the number of recorded events.

How nearby points contribute

In a common geographic heat-map method, points contribute to a surrounding area rather than appearing only as individual dots. Nearby contributions combine. Esri's documentation explains that radius, optional weights, and constant or dynamic rendering affect how density is displayed. Esri heat-map documentation.

In plain language, the map designer chooses how far each point influences the display and how colors correspond to the resulting values. Those settings can make the same events look like several small clusters or one broad concentration.

Example

Hypothetical: A map contains 60 service calls concentrated along three nearby streets. With a small radius, the display shows three narrow bands. With a larger radius, those bands merge into one broad colored area.

No new calls were added. The visual change comes from the display settings. A reader comparing screenshots would need the same radius, map scale, color rules, and filters before treating a larger colored patch as increased activity.

Common confusion

A heat map is not automatically a statistical hot-spot analysis. A bright area indicates high intensity under the chosen visualization; it does not by itself establish that the concentration is statistically unusual.

Nor is it automatically a population-adjusted crime rate. A map based on call points shows the concentration of included calls. Calls can include many kinds of service activity, and the display may not account for population, visitors, or reporting differences.

Reading the settings and source

Check the period, event type, counting unit, and whether points carry equal weight. A map weighted by incident severity or another attribute answers a different question from one where every point counts equally.

Also inspect location precision. Multiple records assigned to the same generalized location can create an apparent concentration influenced by masking. Missing coordinates can leave some recorded activity off the map entirely.

The legend should explain whether color values stay fixed or adjust to the currently visible area. When they adjust, zooming or panning can change the colors without changing the underlying events. Use the display as a summary of the specified data and method, rather than a standalone label of neighborhood safety.

Sources

  • Esri: Heat map symbology — Describes relative density, radius, weights, and constant versus dynamic rendering. The street example is hypothetical.