Silva, Ademar Barros da, Ricardo Seixas Brites, and Antonio Raimundo de Sousa. 1999. “Characterization of the Physical Environment in the Quatro Bocas Watershed in Angelim, PE, and Its Quantification by a Geographic Information System”. Pesquisa Agropecuaria Brasileira 34 (1):109-17. https://doi.org/10.1590/S1678-3921.pab1999.v34.5145.