A feature allowing map makers to set altitudes and filters to show the topography in different styles. This could work well enough in 2D and should absolutely be added...

but I would love to see a fully rotatable 3D map maker on Inkarnate someday although I know that's unlikely; A top down 3D topographical map could still be possible.

Not only would a topography map look really cool it would be helpful for figuring out the flow of rivers and roads.

Below are some of the many styles that this could look like for both 2D and 3D top down