Question: 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
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 point dataset.
Attachment: screen shot
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