standard What is the Difference Between a Heat Map and a Hot Spot Map?

Share:

  

While they look similar and the terms are often used interchangeably, heat maps and hot spot maps are not identical processes.  Both processes are used to visualize geographic data in order to show areas where a higher density or cluster of activity occurs.  For both types of spatial analysis, a color gradient is used to indicate areas of increasingly higher density.

To create a heat map, point data is analyzed in order to create an interpolated surface showing the density of occurrence (learn more about heat maps).  Each raster cell is assigned a density value and the entire layer is visualized using a gradient.  The end visualization which affects how the data is interpreted by the viewer is a subjective one.  The two maps below show the same heat map analysis but with different number of class and cell ranges to set up the gradient.

fortune1000-heat-point-us

fortune1000-heat-kernel-us

Hot spot analysis uses statistical analysis in order to define areas of high occurrence versus areas of low occurrence.  Since hot spot areas are statistically significant, the end visualization is less subjective.  The designation of an area as being a hot spot is therefore expressed in terms of statistical confidence.

In the map below, hot spot analysis using GIS software enabled researchers to locate areas within California where families live who are eligible for the state’s Department of Public Health’s Women, Infants, and Children (WIC) programs but are not receiving WIC services.  The analysis allowed the Department of Health to identify regions with high proportions of unmets needs.

Hot-Spot Analysis in Public Health.  Source: Esri.

Hot-Spot Analysis in Public Health. Source: Esri.

Making Heat Maps and Hot Spot Maps in ArcGIS

Heat maps in ArcGIS are created from point GIS data through the Spatial Analyst extension.  There are two options: point density and kernel density.  To learn more about making heat maps using ArcGIS, visit Esri’s help files for point density and kernel density.

The tool for making Hot Spot maps in ArcGIS can be found in the Spatial Statistics toolset.  Users can find more information including videos about Hot Spot Analysis via the ArcGIS resource site.

Making Heat Maps and Hot Spot Maps in QGIS

Ujaval Gandhi has a step-by-step tutorial about using the heat map plugin in QGIS to make heat maps.  This Stack Exchange post points to at least one resource for finding a QGIS plugin to produce hot spot analysis.

Further Reading

Introduction to Hot Spot Analysis – Informative slide presentation from the Children’s Environmental Health Initiative.

Mapping Crime: Understanding Hot Spots by John Eck, Spencer Chainey, James Cameron, Michael Leitner, Ronald E. Wilson, 2008.  Produced by the National Institute of Justice, this 79 page report takes a look at different hot spot mapping techniques for use in law enforcement.



Like this article and want more?

Enter your email to receive the weekly GIS Lounge newsletter:


2 Comments

  1. Hi Caitlin,

    Great article. I’m so glad you posted this. I was just last week thinking about putting up my own post on this very topic as it’s a misunderstanding I encounter frequently.

    I have one minor modification to the description of Hot Spots analysis though:
    “Hot spot analysis uses statistical analysis in order to define areas of high occurrence versus areas of low occurrence.”

    Occurrence suggests the number of features in a location but that would be similar to modelling density. What a Hot Spot analysis is really doing is looking at statistically significant clusters of high and low values. So a Hot spot is significant clustering of high values and a Cold spot is significant clustering low values. There can be large clusters (high occurrence) of insignificant or randomly mixed values on a hot spot map. I think that’s part of what really differentiates the two methods, the fact that clustering alone is not main indicator of significance.

    Thanks,
    David

    1. Nice article! And thank you for your comment and clarification, David.

      If I’m understanding this correctly, some “Heat Maps” also model more than just density. A “kernel density” analysis can take into account the values (or weights) of the points as well as their locations. (In ArcGIS this is input as the “population field”. )

      One chief difference in this type of “heat map tool” and the “hot spot tools” mentioned above seems to be that heat map tools use raster data analysis, and hot spot tools use vector data analysis.

Post a Comment

Your email address will not be published. Required fields are marked *