I just finished another waterpark cartoon map. I probably have an advantage in this genre in that my degree is in architecture. So, when clients supply reference for a project, I have experience in interpreting the architect's plans into 3D. Of course, I'm doing it in exaggerated fashion to make a fun presentation.
There is an incredible amount of detail that goes into these projects. Many cartoonists are accustomed to working in minimalist styles. It takes a special patience to do this type of work.
When clients furnish photos of an existing park for reference, it's funny how sometimes they will send me the exact opposite side of a view from what I'm drawing. I guess since they are so familiar with their park, they think the most common view from the sidewalk is what I need to work from. But if I have to draw the south side of a building and they've given me the north side, I can't just make up what the other side looks like! Same with rooftops. Lots of times I'm furnished with a pedestrian view of a building that doesn't show the roof. And I'm typically drawing a bird's eye view with these maps. So I have no idea what to indicate for the rooftop!
Thankfully, Google Earth is making my work easier these days with updated aerial photos of most places in the world. I can check out most of these places and, if the resolution is high enough, see a lot of the details the clients may not have on hand.