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here's a map of a country with a red border: https://upload.wikimedia.org/wikipedia/commons/1/13/Congo_Kinshasa_Topography.png
i've imported the .png and now want to clip it to just show what's inside the red border.
tracing results in a huge complicated mess of paths and nodes that basically cause inkscape to hang when i try to intersect/difference them with pencil-drawn paths to try to isolate the border.
i feel like i must not be approaching this correctly, what's the right way to do it?
Hi there and welcome to GDSE.
As you might know the image you have is a raster image which consists of pixels.
Inkscape is a vector drawing application. You can place/import raster images, but you can't directly manipulate the pixels.
As you have experienced your image is way to complicated to do an automated trace.
I recommend you to do one of the following:
Open the image in a raster image application (Photoshop, GIMP etc.) and erase/mask the unwanted area manually (there are many different ways to do this).
Use Inkscape to manually trace the contour using pen tool and then use this shape as a clipping mask for the image.
Find another similar image in svg format (which is a vector based format). Open it in Inkscape and delete the unwanted paths.
The red border is part of the PNG. It's not a vector, so you can't use it as a clipping mask. It's not possible. Inkscape is a vector image editor.
However it is possible to add a vector clipping mask to a raster image in Inkscape. But the process is manual, and involves drawing the clipping mask manually.
Here's a quick example. I have drawn a closed shape filled with semi-transparent orange so you can see it. I select both the raster and the path, then clip it.
a color multi scan trace isolates the red (i used 24 colors but i think you could use less). i found the red one, moved it to another layer, and deleted the rest. then i broke it apart, found the resulting path for the contiguous border, moved it to another layer, and deleted the rest. since the border isn't a closed path (there's a little opening at the coastline), i then had to use the pencil tool, path intersection/difference operations, and another break apart, etc, to get rid of extraneous nodes. then a linked offset, edited its radius to -0.5 in xml editor, and i had a perfect clip.
On the page, where your PNG can be found, there is a SVG file too, two pictures above.
I would download this one, and see, whether the details are fine enough for my needs.
