Why is it when you look at the UK map that the London area is a different colour?

Question

Not all maps, but i've seen certain maps where, particularly the London area, is a different colour. Why is this?

Answer 1

Because it indicates the vicinity of London.

It may also mean the area of Greater London. Most likely it just shows how big is London on UK's map.

Answer 2

Satellite Map- Density Build up

Printed Map- Capital significance

Answer 3

Assuming you are talking about satellite maps, it might be something to do with the fact that London is more built up/ less green space compared to the rest of the country - this effect can be seen in all urban areas but just more noticeable with london cos it is so big.