Lake Mead as 30 m cells keeps its area within 0.02 percent. Its shoreline grows 18 percent.

Vector data stores shapes as points, lines and polygons. Raster data stores a grid of cells, one value each. Turn a lake into cells and its area barely changes, but every curve becomes a staircase, so length measured on cells comes out too long. Once data is a grid, map algebra does math on every cell at once.