Marabá Study site
To transform each selected variable into a population indicator, the occurrence of the districts3 in the municipalities was assumed to be evidence of human presence related to population distribution. Each variable was studied individually to explore its relationship with the distribution of all district seats in Pará state. From the frequency analysis of distance between district seats and rivers, it was observed that 90% of the districts are located up to 17 km from rivers; 50% are less than 3.5 km away from a river, and the average distance is 6.81 km. (Figure 4a). Regarding distance from roads, 90% of the districts seats are less than 127 km far from roads, and 50% are less than 27.5 km away (Figure 4b). Pará state is mostly flat, with slope values ranging from 0 to 7.3%. It was observed that 90% of the district seats had an average slope of less than 2%, 50% of the districts had average slopes of less than 0.27% (Figure 4c).