Well, I can see that you are not well informed about overpopulation.
Space is the least problem.
Food and poverty the things we need to worry about.
Africa's overpopulation problem tends to be caused by poverty. People do not have the ressources to get their shit done etc
In China the problem is the amount of food. 20% of all people on this planet live in China.
Going with “I'd assume city expansion” to solve the problem is, uh, not very accurate.
http://www.ers.usda.gov/Publications/AIB775/

So, I ask again:
How could it possibly be solved without abortions?

I am trying to get this discussion on a less abstract level.
If you want abortion to be abolished without proper solutions it is not going to work.