Lab: Firefly Mapping

With credit and thanks to John Nelson for his posts on the topic.

Firefly maps, in the words of John Nelson, “tricks normal people into realizing how much they like maps”.  They’re an eye-catching way to represent point data (and sometimes other kinds, but we’ll focus on points here).

For inspiration and general techniques, please see John Nelson’s overview.

A bit of Googling will find a Firefly starter pack for Pro, but the basemap it provides is a cantankerous thing that breaks often in our lab setting, so you’ll find instructions below to make your own.  You will want to download the premade Firefly style, however. To bring the premade images into Pro, use Picture marker as your symbol type and browse to where you unzipped them.

The data for this lab should be a point feature that coalesces in some areas and has a lot of dots. Population-based data is great for this, but there are plenty of other datasets out there that will have similar effects. Suggestions include Starbucks locations, Lord of the Rings filming locations, weather stations, farmers’ markets, Bigfoot sightings, etc. Choose something of interest to you and try it out – the main point is that the dots need to be clustered in some way, to maximize the impact of the glow (see John’s examples).  Some good data sources are POI Factory and GPS Data Team.

The dot size should be relatively small – the firefly effect will enlarge it, and the purpose is not to see individual dots so much as the overall pattern. Also, too large and the dots will get pixelated.

Preparing the Basemap

This is just a starting point – feel free to tinker with the settings once you have it all set up.  The idea is to have a subtle background for your fireflies, with just a hint of figure/ground help.

Note: If you’re not one of my current students, check out Hacking the Firefly Basemap instead, and skip to the next section.

  1. Grab the data from the Google Drive (  Unzip into your Originals folder, as usual.
  2. Set your data frame background to Black (Properties > General), and your coordinate system to something for the US that preserves area.
  3. Add USeast.tif and USwest.tif to your map.
    1. Group these two layers (select both, right click > Group) and rename the group to Color.
    1. Set the group to 80% transparent.
  4. Copy the Color group, paste, and rename as BW. 
    1. Move it to the bottom, and set it to 30% transparent.
    1. Symbolize each layer in the BW group as Stretch, and use the default grayscale ramp that comes up.
  5. Add LatLongOceans to your map.
    1. Symbolize as Unique Values, using the field DEGREE5.  Remove all values, then add back in just the Y value.
    1. Symbolize in bright blue, 0.5 pt and 80% transparent
  6. Copy LatLongOceans and paste as LatLongOceansGlow.
    1. Move LatLongOceansGlow underneath LatLongOceans.
    1. Adjust to 5pt and 95% transparent
  7. Add the Coast layer to your map.
    1. Set the color to No color and the outline to Sahara Sand, 0.5 pt, 75% transparent.
  8. Copy/paste as CoastGlow and move underneath Coast.
    1. Adjust to 3pt and 95% transparent

You should now have a snazzy but low-key basemap for your point data. 

Pro Tip: You’ll need to repeat setting the data frame background to black in your Layout also, or your map will look washed out.

Working with XY Data

Remember that most latitude and longitude values collected via GPS or from an internet map service are in the geographic spatial reference system WGS 1984. When adding the data to ArcMap/Pro, the software reads the decimal degrees but has no context for which spatial reference system to use, so it will always assume it should be the same as your data frame. You’ll need to specify WGS 1984 when you use the tool.

  1. Bring the file into your map, right click and Display XY Data, and make sure to specify the coordinate system (don’t trust the default, even if it looks right!). Click Run when done.
  2. Recall that the Events file created is a temporary layer, so export it as a shapefile to your working folder. Specify the data frame as the coordinate system, or use the Project tool to set the correct coordinate system after export.
  3. Remove the .csv and events layers from your map, and the old version if you reprojected.

Making Fireflies

  1. Download the firefly style from John’s blog into your Originals folder
  2. In Catalog, right click on the Firefly style (looks like a painter’s palette) and select Add Style
  3. Click your point symbol, and you should see the fireflies in the Gallery

What to Turn In

A Firefly map, 8 ½ x 11, printed in color for critique and submitted as a PDF to Canvas.


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