A line on a map that connects points of equal elevation based on a vertical datum, usually sea level. A spatial data model that defines space as an array of equally sized cells arranged in rows and columns, and composed of single or multiple bands. Each cell contains an attribute value and location coordinates. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are contained in the ordering of the matrix. Groups of cells that share the same value represent the same type of geographic feature. A vector data structure that partitions geographic space into contiguous, non overlapping triangles. The vertices of each triangle are sample data points with x, y, and z -values. These sample points are not connected by lines to form delaunay triangles. Tins are used to store and display surface models. Digital elevation model: a dem has cells or pixels, each of which contains a single elevation.