Streamline chapter 3

[martinfleis]

Slides are a bit too abstract and slightly repetitive.

Hands on in chapter 3 is a bit suboptimal in terms of flow.

• Try sticking to a single dataset across
• Move overlay beyond "Advanced" or remove it altogether

Exercise, as written, asks to create some not so great maps, esp. the map with smallest. Plus there could be a pointer to contextily for tiles in static maps.