Currently our User Manual describes how to choose between the pre-installed map themes:

https://docs.kde.org/stable/en/kdeedu/marble/map-views.html

But it lacks a paragraph that points out how to download further map themes, including map themes of other planets. It also lacks a description of the available projections and how to switch between them.

Please add a chapter right after "Chapter 3. Choosing different map views for Marble" which explains:

- How to download and install further map themes - including a rough description of available topics and possible use cases.

- How "Download Maps" allows to display other planets and moons and how the user can swtich between them

- Which projections are available in Marble. Describe the use case and how to switch between them.

Please add screenshots for each topic and honor the screenshot guidelines that are available for the documentation.