This lecture introduces the fundamental role of relief in modeling Earth's surface phenomena, emphasizing the importance of topographic variables in spatial analysis. It covers the definition of altitude as the vertical distance from a point to the Earth's geoid surface, along with three measurement methods: geometric leveling, photogrammetry, and laser scanning altimetry. The advancements in technology, particularly laser scanning altimetry, have enabled the production of highly precise digital elevation models, facilitating the study of microrelief by various professionals like biologists, geologists, archaeologists, and urban planners.