ABSTRACT
Geographic data are inherently a form of spatial data because they concern the physical dimension and have a spatial location in the real world.1 These data tell us information about our world, and their locations are defined by using Earth-based locational coordinate referencing systems. Two common systems of coordinate georeferencing are the spherical and Cartesian systems (Figure 2.1). The spherical coordinate system describes a position on the surface of the Earth in terms of a pair of readings in northing (parallel or latitude) and easting (meridian or longitude). The latitudes (y coordinates) range from 0° to 90° in the northern hemisphere, starting at the equator and moving toward the North Pole. Similarly, the values range from 0° to −90° in the southern hemisphere, moving from the equator to the South Pole. The longitudes (x coordinates) range from 0° to +180° in the eastern hemisphere, starting at the prime meridian in Greenwich, England, and traveling eastward across Europe, Africa, and Asia. The range in the western hemisphere, also beginning at the prime meridian but traveling westward across the American continents, is from 0° to −180°.
