I have a raster map that has red areas in it. I want to extract the red areas as a polygon FC for spatial analysis purposes (find where the red polygons overlap a different polygon FC).
Unfortunately, the source vector data isn't available from the government organization that produced the map (1980). So I'm hoping to extract the red areas using GIS tools instead.
I've georeferenced the image in ArcGIS Pro. Next, I think I need to:
What's a good way to do that?
ArcGIS Pro 2.6.8; Spatial Analyst Extension
Is there only one red? or a range of red colors?
If you know its class value, you can extract by its value
Extract by Attributes (Spatial Analyst)—ArcGIS Pro | Documentation
then use
Raster to Polygon (Conversion)—ArcGIS Pro | Documentation
ensuring that you use the same raster extent, cell size and alignment as the input raster.
The generated polygons might not be to your liking, so you could convert your other polygon file to raster and do the analysis within the spatial analyst (eg Combine etc)
Here's what I have so far:
In Adobe Photoshop 2023:
I did many of those steps multiple times to get the desired effect.
Now, only the red areas are shown, as a single color: R:255, G:0, B:0.
Next:
Fix the georeferencing. It turns out it wasn't as well aligned as I thought.
Having trouble fixing it -- I can't seem to get the entire map to be properly aligned.