Flag of Alajuelita canton, of San José province, Costa Rica.
Own work, I have seen the proportion of the bands with thinner green and wider yellow (1:2:1), however, the use seems to be interchangeable between that and the flag flown outside the Municipality which seems to have the three bands of the same size (1:1:1) like in [1]. Please update if there is a proper source with the correct proportions. 

This file was derived from: Bandera Alajuelita 2.png:
Roqz