I have a choropleth map of plankton distribution in the ocean that I am digitizing. However, as you can see, there are many features within features creating rings, almost like mountains on a topographic map. I'm using QGIS to digitize this map.
At the moment my game plan for digitizing these is to:
Digitize the innermost rings using Freehand editing plugin - "> 500" according to the scale
Digitize everything surrounding those - "250-500" according to the scale
Clip all "> 500" patches out from the "250-500" shapefile
So on and so forth. This does mean I'd have many shapefile layers and much clipping to do, though it seems faster and less error-prone than simply tracing out each feature and contour line by hand.
My question is - before I commit too much time and effort to this clipping technique, does anybody in the community know of a better or faster way of doing this? Or is simply manually tracing each contour line the best way to go?
I'm worried that I may be reinventing the wheel, trying to figure out a problem that may be common knowledge to somebody who has much digitizing experience.
PS - if there is a better term for this map than "psuedo topographical choropleth", and I assume there is, please update my post/let me know! I don't know what this style of map is called.