[GIS] How to disperse clusters of proportional markers or polygons

arcgis-desktopclustering

I am mapping a set of points in ArcMap that are symbolized using proportional marker symbols based on a numeric field value. The scale of the map has lead to alot of the point markers overlapping.

current cluster

I would like to disperse the markers so that they are not overlapping. A random dispersement would be fine, preferably with control over the spacing between the dispersed markers. It seems that proportional symbols can't be converted to representations (else I could have used the Cartographic Refinement – Disperse Markers tool).

I could buffer the points by the numeric field to create polygons instead of using point markers to get around the representation issue, but is there a way to disperse polygons away from each other so they are not overlapping (similar to the functionality of the Disperse Markers tool for points)?

I'm using ArcMap with an Advanced License. Thanks

Best Answer

Check out this link: http://blogs.esri.com/esri/arcgis/2008/08/01/how-to-scatter-marker-symbols-for-stacked-or-clustered-point-features/

I think that might help you with what you are hoping to do.

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[GIS] way to “disperse markers” across multiple point layers

I don't see any direct way, but it'd be easy enough to perform a Merge (docs) on the input data, mapping a field to retain information about the origin layer. In some cases, you may be able to use this merged layer directly, and symbolize the different features within it. Perform disperse markers on the merged set, and use as-is or split on the unique features mapped from fields.

If you only care about making them non-overlapping, and not their specific location, you could displace each layers positions by some systematic amount below the actual mapped resolution of your data, so that they were naturally clustered when mapped. For example, if you had layers A and B, you could make the least two significant figures of A something independent from B:

layer    lat     lon    rule perturbed_lat perturbed_lon
    A   33.0  -120.0  +0.033        33.033      -119.967
    B   33.0  -120.0  +0.011        33.011      -120.989

Now if you perform disperse on one of these layers, the data will already be clustered into distinct areas of the map. You'd have to play with the offset values and figure out an appropriate offset. But this approach would give you a systematic way of preventing collisions between layers.

ArcGIS Desktop – How to Hide Internal Polygon Boundaries

I cross posted this question on Esri's Ask A Cartographer site. They pointed me to a mostly-suitable workaround: use Symbol Level drawing in general and Dissolving polygon boundaries using symbol level drawing in particular. Likely what Craig was pointing at earlier in his answer. I've seen the dialogs and help topics before but hadn't dug into them because the examples are about cased lines and I didn't understand how the same principles could be applied to polygons. With the v10 help they've greatly expanded the examples and procedures. Although written for a v10 audience it should help v9.x users as well as it hasn't changed that much.

I did finally get Symbol Levels to work with our data in situ (no duplicate feature classes created, no attributes added). There are few inconsistencies in the symbol level interface which add confusion, which I'll mention here (a.k.a. "watch for submerged rocks" and "here be dragons"):

Boundaries don't dissolve when marker or picture fills are used, only plain and gradient fills work
Sometimes editing a symbol causes it to jump to the top of stack (under "Advanced > Symbol Levels") and it's join/merge state change to unchecked.
Sometimes the advanced settings won't "take", try changing the stack order and various applications of enable/disable join/merge.
After enabling Symbol Levels Occasionally the "apply color ramp" step (#17) doesn't work at all. The symbols stick with what is defined in the upper most Edit Symbol dialog. An Arcmap reboot seems to cure it.

A workaround for using marker/picture fills, dissolving all internal boundaries, and drawing outermost perimeter of all objects ("ordinary high water mark" in the sample data (linked to in Q)) is to:

add the layer a second time in the TOC, below the marker/pic fill layer,
Use "Single Symbol", plain fill, enable Symbol Levels, do the same double layer trick as above under advanced symbol properties
and enable both Join and Merge checkboxes (another bug here: sometimes the []Merge box is not enabled until after you go to advanced symbol properties editor.)

Develop the habit of always doublechecking the stack order and the join merge properties. Just because you told it to do/not-do X doesn't mean it actually remembered.

So in summary,for cartographic purposes Symbol Levels with join & merge properties is a workable if quirky analog for Arcinfo Regions. For analytical purposes like "query surface area of ordinary high water" you'll still need to do some geoprocessing and generate duplicate data.

(UPDATE) It is possible after all to use picture symbols, symbol levels, and a single ToC layer. You set your tongue to the right, just so, stand on one leg (doesn't matter which), and face the moon. From here get a map package illustrating two working methods (Lake-cartography-symb-levels - update.mpk).

see full size image

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[GIS] way to “disperse markers” across multiple point layers

ArcGIS Desktop – How to Hide Internal Polygon Boundaries

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