This lecture introduces geographic information systems and covers discrete variables, spatial properties, autocorrelation, basic elements of digital elevation models, derived products like slope, orientation, curvature, flow lines, watershed boundaries, continuous variables, sampling, contour lines, interpolation, data layer interactions, and thematic variables derived from altitude models. It also explores visibility analysis, shadow casting, solar radiation analysis, drainage lines, watershed limits, flood zones, rockfall hazard mapping, and schistosomiasis transmission risk assessment.