Perhaps you should try some spelling variations:
population center » population census, population censuses, population change
5.2 communication » 3.2 communication, 6.2 communication, 2.2 communication
4.3 developing » 3.3 developing, 1.3 developing, 7.3 developing
technology 1 » technology _
1 population » 2 population, 4 population, 2.1 population
center crec » center prcec, center area, center eric
costs 4.3 » costs 4.2, costs 4.4, costs 2.3
crec 5.2 » clsc 5.2, spec 5.2

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

• Adding a wildcard symbol may retrieve word variants: technology 1 population center crec 5.2 communication costs 4.3 developing _ african.*.