Great question. This won't be a definitive answer by any means, but here are a few key things I would keep in mind. Note that some of what I'm about to say has already been covered very well in the following two articles:
How Should Your Mobile and Desktop Sites Differ?
Your Content, Now Mobile
Which information should be left on the map?
Short answer: All of it. Users of mobile devices should have (and will often expect to have) access to the same information as users of non-mobile devices.
Long answer: If the "full" version of a screen would prove too cluttered or otherwise unusable on a smaller device, a good approach is to provide a settings menu (often via a gear icon in the upper right corner) which lets the user toggle various categories of information on or off. This is similar to the functionality of the layers icon in your last example (Google Maps, I believe).
For any building, bathrooms and emergency exits should always be on by default.
What should be simplified (rooms collapsed into general areas)?
Going with the Google Maps example again, a good approach here is to show high-level detail when the user is at a high zoom level (e.g., just the major department store names in a mall, or major cities & roads on a map), but then provide lower-level detail as the user zooms in (e.g., smaller store names in a mall, or smaller cities & roads on a map).
The rule of thumb here should be: What can the user clearly see at this resolution and zoom level? This approach could use breakpoints at various resolutions or zoom levels, much like most responsively designed web pages do. And if you can provide a "large text" mode too (with slightly different breakpoints to account for the extra room taken up by labels), that will be a huge benefit to users with bad eyesight.
How should colors be picked?
I'm not aware of any significant differences in color display between monitors and mobile device screens. The usual aesthetics and UX design factors apply to both. But you might want to take into account how color blind people might see your map, using the resources below. (This would of course apply to both mobile and non-mobile maps.)
Try Vischeck on Your Image Files
Colorblind Web Page Filter
What level of interactivity is expected from such map (what is tappable?)
To some extent, this behavior aspect is similar to the ones above in that the same level of interactivity should be provided on both mobile and non-mobile devices, and the design choices you make depend more on a solid UX approach in general than on device-specific guidelines.
That being said, here are a few "desktop-to-mobile" conversion tips that have worked well for me in the past:
- If you have a right-click action on your desktop app, trigger the
same action with a long-press (a.k.a. "touch and hold") on a mobile
- Make sure that tappable areas are big enough to easily hit on a touchscreen, and sufficiently sized or spaced that the user doesn't accidentally hit a nearby tappable area instead. (There are various conflicting guidelines on what exact sizing and spacing this entails; manually testing with various devices will help you pinpoint which sizing and spacing works best for your particular app.)
- Double-tapping (or touching and spreading two fingers) should zoom in, when applicable. Be sure to keep the tapped location visible (e.g, if they double-tap near the edge of the map, don't keep the same center point when you zoom in, or the place they tapped will no longer be visible.)
- Pinching with two fingers should zoom out, when applicable.
Stand on the shoulders of giants! Find a few mobile apps that do a great job of providing functionality similar to what you need to provide, and then emulate their approach. Many of the more popular built-in iPhone apps and Android apps are usually great examples to follow. Plus, any similarities between those apps and yours will be an immediate UX win, because users will already know how to interact with your app without having to consult your help section. (Oh yeah, and definitely provide one of those too, so users can easily find out about all the features that your app provides, and how to access each of them.)