Perhaps you should try some spelling variations:
population center » population census, population censuses, population change
4.2 communication » 4.2 communications, 3.2 communication, 4.1 communication
technology 4 » technology _, technology 1, technology 3
4 population » 2 population, 2.1 population, 2.2 population
4 developing » 3 developing
center crec » center prcec, center area, center eric
crec 4.2 » drc 4.2, hsec 4.2
costs 4 » costs _, costs a, costs 4.2

You may be able to get more results by adjusting your search query.

• Adding a wildcard symbol may retrieve word variants: technology 4 population center crec 4.2 communication costs 4 developing _ african.*.