Lesser density would make it possible to be larger than Earth and still have tolerable gravity. The larger science issue is with diet. We require a certain amount of a good number of metals for our health. An environment, and hence a diet, too low (or in most cases, too rich) in any of these elements will prevent human thriving. So, this is definitely in the "soft" science fiction category, but that's fine. It's a fictional map, not a research paper on potential exoplanet colonization.

On the map-making front, I do wonder what effect a low density planet would have on geological processes. I expect that if you did get plate tectonics, they'd end sooner than on Earth. If nothing else, you're down heating from radioactive heavy elements. You'd probably need to get a lot deeper into mineralogy of the planet that you'd want to in order to figure out things like maximum mountain height and such. Interesting topic, but nothing to tackle in a monthly challenge!