I'd like to use dot density to display some data in Arc, but the areas (polygons) I'm displaying it for are so small in some cases that I suspect the pattern is being misrepresented.

If several small areas fall within the size of one 'dot' for example, will ArcGIS suitably aggregate the data from multiple areas to display a dot? If there isn't enough data (for example because the number of households is below the dot quantity), will those be aggregated into neighbouring areas?

If I am concerned about misrepresenting the data in this way, is there a way to work around this?

  • 2
    It would be helpful to include a screenshot of the problem.
    – Aaron
    May 13 '15 at 16:04
  • @Aaron is right about an image-example. I also assume you mean point density rather than "dot"; and can't understand how multiple polygons can fall within the size of a "dot" (e.g. point which has no dimensions)
    – dof1985
    May 13 '15 at 21:39
  • 2
    @dof1985 no, he means dot. It's a type of map, and in ArcGIS is expressed as a Quantities symbology type/style: resources.arcgis.com/en/help/main/10.2/index.html#//… Like any other symbology, if you set the size too large (pts like font size) it may well cover neighboring features. This is particularly an issue in Graduated/Proportional symbol style maps of small polygons with high values (ie population of northeastern seaboard states like Delaware or Rhode Island).
    – Chris W
    May 14 '15 at 0:38

No, it does not aggregate adjacent enumeration areas (polygons) into a single dot. If there's a dot to show, it's shown, and if the symbol size is too large or value count too low then the dots will simply overlap/coalesce (potentially leading to a solid polygon shape of the dot color). For areas that don't meet the minimum value, no dot is shown and the values are not aggregated to adjacent polys.

Your two solutions/workarounds are to increase the map scale (perhaps with insets), or do some manual aggregation with your enumeration areas - potentially with explanatory notes. Alternatively you just have to experiment with different size/value combinations to find the best result that represents the picture/story you're trying to tell with the data.

  • Thank you for the answers ArcGIS help doesn't give :) I used a more aggregate geography and I'm convinced the picture is more accurate as a result. May 14 '15 at 12:46
  • Ultimately I guess you could solve this by converting 'dots' to a point data set with each dot on a polygon centroid (or better yet a population weighted one). Then use representations and disperse markers to prevent dot overlap. A very long workflow considering you would probably need to iterate a few times to determine the best dot value, so I didn't take this route, but there's probably some mileage in creating software to do just that, if somebody wants to! May 14 '15 at 12:49

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