Geography

I'm struggling with these two questions, so if anyone could answer them for me or give me some pointers I'd appreciate it.

Q1. Suggest 2 reasons it is difficult to accurately measure the urban population in countries with a lot of slums.

Q2. Explain reasons for the distribution of megacities across the world. [6marks]

q1: Potentially go along the lines of people who live within slums won't have access to hospitals/medical centres for birth/death measurements? If they don't have money/travel etc for certificates to be created, could lead to a lack of demographic information. Can't really think of another reason, asides from how do you measure the size of the slum? You can't really decide on the population without setting an area of a slum...

q2: (This is about 7 years ago for me so this may take some time) Going along the lines of economy, where the work is, even aspects of physical geography e.g. rivers/canals, ocean routes which accounts to trade. Majority of the megacities you can think of have harbours and big financial centres. A contrast from the original megacities (New York and Tokyo) to more recent ones, where the work was needed for industrialisation etc.

The only downfall to the megacities is how global politics has affected the distribution of megacities but I'm not sure if this would count in a geography question anymore!