Question: Can anyone recommend open source map-making / site design software?

I'm looking for software for making small-scale maps / designs. Say for example I wanted to map out a small-ish plot of land with various markers indicating features of the site. Another requirement is that is must have the capability to depict elevation. Others have recommended map-making software for dungeons and dragons, but of the ones I can find they are either paid / subscription models or they strictly adhere to a grid system that makes it impossible to use for my purposes.

Does anyone have some good recommendations?

Edit: It doesn't have to be a single piece of software necessarily. If anyone has recommendations for a particular workflow (like for example if you know some good open source drawing software I could use to draw over the top of a topographic map) I'm interested in that as well.