Small vs big Polygon overlap on a Map Question

[PROBERT68]

Hi ,

I have been searching  or google  for a map that shows two polygons with no luck. What I want is to look at a map or maps  where there are two polygons that overlap each other.  What I mean is if there is a small polygon that is under a big polygon. Are there examples that can I look at ?  and if so what is the workflow for that ?

I hope this is not a hard question to ask .

[shan_sarkar]

Hi @PROBERT68 ,

Do you mean you want a bigger polygon to overlap with a smaller polygon, with the bigger polygon being the top most layer and the smaller polygon being the underlaying layer?

If you using simply looking for an sample you can use the Template data that comes along with the ArcGIS Desktop installation. Ideally the data is located at C:\Program Files (x86)\ArcGIS\Desktop10.8\TemplateData.

This contains 2 datasets one for the basic world data and basic US data with state boundaries and county boundaries.

I hope this helps.

[PROBERT68]

Yes, you are correct .

[DanPatterson]

2 quick methods.

- symbolize the polygons with no fill, just an outline

- produce a featureclass which sorts the geometry based on the shape_area field in descending order or area, so big things get mapped first then smaller things on top.

Sort (Data Management)—ArcGIS Pro | Documentation

[PROBERT68]

@JohnMNelson 

Your thoughts on this for Cartography or Map-making ?

[JohnNelsonEsri]

occlusion is a persistent challenge in cartography. somethings bigger things just cover up the smaller things. if you have a map where this is happening, you could consider some options for the polygon fill. the most basic option is to set the fills to be semi-transparent so that overlapped content is still largely visible. another option is to experiment with blend modes for the topmost layer and make a clever legend describing what the overlapping areas look like. but i would consider using a hatched fill for your layers so that they were visible in all cases. for example, i used hatched fills of different colors and hatch orientation to show individual, and overlapping, species ranges in this map: https://adventuresinmapping.com/2016/06/09/how-to-sharknado-map/

[PROBERT68]

Thank you John. So is that the word you token as "Occlusion" maps where there is a small polygon is hidden by a bigger polygon ? 

[JohnNelsonEsri]

yes, occlusion is just the general issue when one thing covers up another thing. when working with several layers it can become a challenge. it's a very large challenge in 3D mapping, where elements in the foreground tend to obscure elements in the background.

[PROBERT68]

Has that word been around in years or is it just pop up a new terminology recently.  I need to grab a cartography book  HA HA HA ....

[PROBERT68]

I couldn't find the book I have but I did went over here. https://oer.galileo.usg.edu/geo-textbooks/3/ 

and did not find any word you mention "Occlusion"