Smart Mapping: Heat Map
Use heat maps to reveal patterns within overlapping point datasets
Getting Started with Density
Point datasets with a large number of dense features inevitably overlap, hiding any potential meaning within the data. That's where heat mapping comes in for the assist.
What is a heat map? A heat map uses the features in the layer to calculate and display the relative density of points on the map as smoothly varying sets of colors ranging from cool (low density of points) to hot (many points) - hence the name heat map.
They are effective for displaying layers that contain a large number of points. Heat maps are particularly helpful when many of the points on the map are close together or overlapping, making it difficult to distinguish between features. This is especially common when points are viewed at multiple scales. Small scales make large, dense point features nearly indecipherable, forcing the viewer to zoom in and lose any potential pattern hidden within the data. Additionally, heat mapping is also great for event-based data, such as traffic violations, where it is likely that points are coincident in the same location. Mapping the relative density of points allows us to answer questions like Where are the most points located? or Where are high and low values for a particular attribute clustered?.
Create a Heat Map
Smart mapping helps you create beautiful and informative maps, quickly. It sets the cartography of your layer based on the significant values within your data. Smart mapping lets anyone quickly discover patterns from attributes in their data and make meaningful maps from them. The heat map drawing style can be broken into 2 simple steps:
- Select the Heat Map style
- Explore the Style options to adjust color and density
To start, you'll need a point layer with a high number of features in ArcGIS Online or ArcGIS Enterprise open in Map Viewer . Let's walk through an example:
To begin, it is good practice to change the default basemap to a neutral option such as dark or light gray canvas or the human geography basemaps.
This allows the points to become the focus of the map without the distraction of too much background color.
With your point layer selected, open the Styles pane on the right hand side.
Smart mapping recognizes the layer as points and will provide smart default style choices that are appropriate for the data.
Select the Heat Map option.
You will notice the map immediately updates to the heat map style.
Let's explore how to customize the map beyond the defaults by diving deeper into the style options.
There are many different color ramp choices for your data's story. It's important to select a ramp that is also appropriate for the basemap.
Tip: Color ramps can be filtered to show ramps designed for light or dark basemaps, or color-blind friendly.
For this example, choose a color ramp with a dark low color and a bright high color. This will emphasize the denser clusters of points - areas with more traffic accidents.
Adjusting the position of the two handles on the color ramp slider will change how the colors are applied to the density surface.
Lastly, the cluster size can be adjusted to be larger and smoother, or smaller and more distinct, using the area of influence slider.
As the map maker, you can decide what settings make the most sense for your data.
If your data contains numeric attributes, the heat map can weight this data to calculate the optimal display. Let's take a look at how weighting affects the heat map by adding the number of traffic injuries.
Choose an attribute field with numeric data to take advantage of weighted features. Note: Strings and date values are not weighted.
Using swipe on the images on the right, you can see that the weighted heat map (right) has more cool spots in the San Francisco, Central Valley, and Southern California areas. Whereas the clusters in Chico, Northern California, are much hotter.
This tells us that there are fewer accidents in Chico compared to the other major urban areas, but the accidents result in more injuries.
Show Both Heat and Points
The heat map drawing style is a simple style to apply to point data. As the mapmaker, it is always important to use your knowledge of the data to make a more powerful map than accepting the defaults. There are some tips and tricks to keep in mind when using heat maps.
Add the point layer again on top of your existing heat map for pop-up information and reference. Increase transparency so the heat map is still clearly visible or adjust the layer visibility so the points only appear when zoomed in.
Starbucks in NY
Avoid heat maps if you have only a few point features; instead, map the actual points.
While smart mapping will come up with a useful default map, don't be afraid to adjust the settings. Don't like your changes? No problem. Just hit 'Cancel' instead of 'Done' and it will revert to the previous setting.
Heat mapping is a powerful style that quickly transforms dense point features into a readable map. With smart mapping providing a strong foundation for the data, it is easy to customize the style further to create the map for your needs.
Try it out today, and when ready share your maps with the hashtag #smartmapping and #ArcGISOnline.
