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I'm trying to map the boundaries between regions which don't necessarily have a hard edge.

For example, areas where languages predominate don't have a distinct edge, but instead have a degree of overlap - people don't suddenly stop speaking a language at a country border. How would you convey this in a map?

Here is an example I found showing tourist regions - I like how they've conveyed that you don't suddenly reach the boundary of a region, but that they are more nominal:

enter image description here

(I suspect that they used something like Adobe Illustrator to create this?)

How can I achieve a similar effect in ArcMap? For bonus points, I'd like a solution which will transfer to ArcGIS Server's JS API.

My starting point is a polygon layer which does contain hard edges - something like this:

enter image description here

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    You'll have to pick your colours carefully, some don't blend that well and others may be very similar. I'm thinking start with a buffer negative a few hundred metres then a distance raster but not sure how to transition the colours from that. In the end I think that you will need a raster to display properly but might need to do some clever maths for the transition. I think it might be best to prepare a raster layer in PhotoShop using the blend (use worlded TIFF and the georeference isn't destroyed).
    – Michael Stimson
    Commented Apr 28, 2014 at 23:57
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    I found a similar requirement at forums.esri.com/Thread.asp?c=93&f=1730&t=303003 but am not certain whether the link from there (blogs.esri.com/esri/arcgis/2008/10/14/…) may lead you somewhere useful ...
    – PolyGeo ♦
    Commented Apr 28, 2014 at 23:59
  • Related questions (particularly the latter): Can shaded relief be “blended” with DEM colour ramp in ArcGIS to produce a more visually dramatic result?, How to vary the transparency of symbols within a single layer in ArcMap?
    – Chris W
    Commented Apr 29, 2014 at 0:14
  • Do the colors need to blend/cross the boundaries, or just fade up to the boundary? Is splitting the polys to separate feature classes by value an option? Without going to raster, I don't think it's possible in ArcGIS to overlap shapes in the same feature class and see both, even with transparency (something that's been driving me nuts for a couple of weeks now). I do have a way to get the soft edges though, and with separated feature classes it should work to blend them together.
    – Chris W
    Commented Apr 29, 2014 at 7:17
  • @ChrisW could you share the method using separated featureclasses? I'm not sure about the other detailed requirements at this stage. Thanks
    – Stephen Lead
    Commented Apr 29, 2014 at 22:35

2 Answers 2

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with your polygons, you could use gradient fill symbols with the buffer style. If your color ramps all fade to white, there will be an uncertainty area along the edges. The percentage parameter is used to tune the display with more or less gradient compared with "full color".

In raster, you can stack your image with an additionnal band (based on the euclidian distance), and add it as an alpha channel.

enter image description here

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    The problem with gradient fills is you get wildly differing results depending on the polygon, as seen in the image - gradient width varies quite a bit. I thought I had a solution - buffer the boundary to create a consistent width shape for the gradient. But it turns out the Percentage is for the shape's extent, a relative measure. There's no way to be consistent unless polys are all roughly the same size. Why ESRI didn't give us the option to use an absolute instead of relative value for the gradient width is beyond me.
    – Chris W
    Commented Apr 30, 2014 at 18:05
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    I also tried to tackle the problem by creating a custom color ramp that faded faster than the default ones do. That didn't work either, since the percentage is by extent and not color ramp width. A custom ramp also doesn't help with blending, since ArcGIS ramps don't support transparency - you can't go to 'no color', you end up with white or some sort of gray. When you enable transparency on the layer, that white or gray still strongly affects the underlying layers.
    – Chris W
    Commented Apr 30, 2014 at 18:10
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This might be overkill for your purposes, but ESRI has a blog post on feathering edges as well...

http://blogs.esri.com/esri/arcgis/2011/11/02/figure-ground-feathering/

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  • This works well but has limitations. I used this effect for waterbodies and some (great lakes) are sometimes too large or too complex to buffer. Map refreshing also becomes issue with many buffer rings.
    – Jakub Sisak GeoGraphics
    Commented Apr 29, 2014 at 17:57
  • Also, this link is to the updated blog post/version of the same method that PolyGeo links to in a comment to the question.
    – Chris W
    Commented Apr 30, 2014 at 17:55

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