The population in cities can change in three different ways, unlike other areas, such as counties, where population can change in only two ways:
- Natural Increase (how many more births there were than deaths)
- Positive net migration (how many more people moved in than moved out)
Cities, on the other hand, can also increase by annexation, or the incorporation of areas that were previously outside the city boundary.
In this post, we are evaluating growth only in terms of the first two elements listed above—natural increase and net migration. When showing population change over two periods, we are comparing the same size area in both 2010 and in 2015, based on the 2015 area.
To illustrate the difference that the third factor, annexation, can make (and thus comparing two different areas), consider two cities who have recently gone through annexation:
- Chamblee grew 140% in area from 2010-2014 due to annexation and, as such, increased 185% in population (when comparing the change in population from the 2010 area to the much larger 2014 area)
- Norcross similarly increased 33% in area, leading to a population increase of 82.5% when looking at the different city boundaries in 2010 and 2014.