If you assume I know little to nothing about QGIS 3.10, but have been attempting with some success to create fictional world maps with it, and that I have very limited (OpenScript and Excel) programming skill, perhaps the imprecise technical nature of my question will make more sense!
I am creating Raster files to serve as DEM files.
My process is to create a a set of polygons (within a multi-polygon shapefile layer) for elevation contours.
I have tried starting the coastline contour as elevation 0, elevation 1 and elevation 10
I have used elevation (contour) intervals of 100
I then use Vector/Geometry Tool/ Extract Vertices and get a series of points along each polygon perimeter.
I use the Processing Toolbox / Vector Geometry/ Add Geometry Attributes tool to create x,y,z coordinates for each point
I have then gone into the attribute table, selected all of the points, used the multi edit tool and set zcoord = to elevation
I then have either created contours from the data, or just used the points themselves with similar results, and completed a TIN interpolation.
You can see the triangles departing the coastline, which produces a raster that doesn't really show the coast at all. I have added a second photo to demonstrate and you can see the triangles jutting off the coastline in the raster file
I am certainly committing some error in this process and wondering if anyone can direct me to a tutorial or provide some suggestions for how to create a more precise coastline.
I have not yet attempted creating a -100 contour around the island and then a 0 elevation coastline.