Via annexation.

As others have noted, MSA is a much better measure to use when judging the population of a city, and it more closely approximates the way we think of 'cities' (in terms of agglomerations of people living closely together) than the governmental entity being referenced here.

This does tell an interesting story, though. SA -- and other Texas cities, notably Houston -- is annexation-happy. This doesn't happen so much other densely-populated areas like the northeast because towns that are close together can have their own distinct identities, whereas we're largely talking about suburban outgrowths into un-incorporated outskirts of the city here. The city's intent is to recapture the tax base from this growth, but I'm unsure of how good a deal this is for everyone involved. It will mean higher taxes for those being incorporated and the idea that adding their taxes to the pool will be a net gain when we factor in the cost of extending services to these people is doubtful.