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symbolize polygon feature as points

November 25 2009 | 3 comments
Categories: ArcGIS Methods, Symbology

We have a building (polygon) layer and I have symbolized the polygon features using point symbols based on the caption field. If I make a selection of this feature and “create layer from selected”, or export the feature the result is again a polygon, but the symbol properties are only always polygon choices. I cannot for the world imagine what I may have done to be able to symbolize the polygons as points. If I change the symbology in any way the feature reverts somehow and can only be symbolized as a polygon???

How did I do this and more importantly how can I recreate it?

Thanks so much

Mapping Center Answer:

Given the phrasing you used, I'm going to first differentiate between symbols, data, and layers, to ensure my explanation has better likelihood of making sense.  First there are three basic kinds of vector features, points, lines, & polygons.  In ArcGIS the symbology methods follow suit, marker symbols, line symbols and fill symbols. The symbols are not stored as data (cartographic representation symbology is the exception to that, but I'll leave that out of this discussion for simplicity's sake).  A symbol is used to draw a vector feature's geometry, but only the symbol type that corresponds to the geometry type.  In ArcGIS layers are a way to store the assignment of symbols for a given feature class; and layers are stored inside Map Documents (.mxd) and Layer Files (.lyr). 

So, I'm not exactly certain of how you created the enclosed image--it's possible to do so with a marker fill, but depending on the size of the polygon the marker may not draw, it's possible to use cartographic representation symbology to do a better job, and it's also possible to label polygons with a marker symbol.  These methods all represent more work for you to both perform, and to explain to others.

The best option and easiest is to use the Feature to Point tool which will create a (centroid) for each polygon, and include the attributes you need to symbolize the points.  This requires and ArcInfo license.  Then you can just use a marker symbol for the resulting points. This is the least amount of work for not just you, but also your organization.

If you don't have an ArcInfo license, you can instead use the Calculate Geometry tool in ArcMap to calculate the X and Y centroid coordinates for each polygon--you will need to add two new fields [type = floating point or double] to your buildings, one for the X coordinate and one for the Y coordinate.  Then in ArcMap open the table and right click on each field's name, and choose Calculate Geometry. 

Once you have those two fields, you can use the Add X Y data tool (on the tools menu in ArcMap) to create a poing dataset.



symbolize polygon feature as points posted by Kalvan Hone on Jan 24 2011 4:16PM
The answer to this question frustrates me. It makes perfect sense to have the option of symbolizing a polygon feature class as points based on centroids without having to make a copy of the data.

I haven't tested this with ArcMap 10, but with 9.3 you can accomplish this using an easy trick. In ArcMap, add a point feature class, any will do, with any point symbology applied. Then, on the Source tab in Layer Properties, Set Data Source to your polygon feature class. ArcMap does not even hesitate attaching a point renderer to the polygon centroids.

With this trick is applied, you can change the symbology, save as a layer file, apply definition queries, label, etc. as expected. I would not, however, count on this as a permanent solution as it appears to be an undocumented feature. Save your newly created symbology to a layer file and keep it handy since at some future point your mxd will very unexpectedly decide to forget how it applied the renderer one day upon opening your mxd and you will have to remove and re-add using the layer file.

If the option is not available for mixing renderers between data types in future releases, it should be IMHO.
You can do this already posted by Aileen Buckley on Jan 25 2011 11:00AM
You can of course symbolize polygons as points without changing the geometry type -- this is what you do when you use Graduated or Proportional Symbols (or even Charts) to render the polygon features.

I tried the method you described in ArcGIS 10 and it did not work for me -- the polys rendered as polygons, not points. But you can still do what you want -- again without changing geometry type -- if you use the Graduated Symbol renderer and set the Symbol Size settings to be equal (e.g., from 4 pts to 4 pts).
Custom Renderers? posted by Tim Dine on Jul 13 2012 7:35AM
I've tried the 9.X version trick for resetting the datasource of a point layer, but you still get the label properties for polygons. My ideal situation would be a renderer that symbolized based on the centroid or true centroid, and some label properties that used the point labeling rules on that centroid.

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