Geospatial data should be geographically referenced ( called georeferenced or geocoded) in a common coordinate system.
Plane Orthogonal Coordinates
One of the most convenient way of locating points is to use plane orthogonal coordinates with x (horizontal) and y (vertical) axis as shown in Figure 1.1 (a) and (b). Mostly a right hand system with the thumb assigned to x and the forefinger to y will be used as shown in Figure 1. 1 (a) while a left hand system may be used in a specific case as shown in Figure 1.1 (b).
In case of raster data, image coordinates (i, j) with the pixel number in horizontal direction (column i or pixel i) and the line number in vertical direction (row j or line j) as shown in Figure 1.1 (c) are commonly used.
Polar Coordinates
A polar coordinate system with the angle (q ) measured from the polar axis (x axis) and distance (r) from the pole is used in some cases as shown in Figure 1.2 (a).
In geodetic survey, a point is located with the azimuth (A) measured from the North and the distance D from a geodetic point as shown in Figure 1.2 (b).
3D Orthogonal Coordinates
Three dimensional (3D) orthogonal coordinates are also used to locate points with the plane coordinates (x, y) and height or depth (z) as shown in Figure 1.3 (a) and (b).
In case of locating points on the Earth on the assumption of a sphere, latitude (j ), the angle measured between the equatorial plane and the point along the meridian and longitude (l ), the angle measured on the equatorial plane between the meridian of the point and the Greenwich meridian (or called the central meridian) are used as shown in Figure 1.3 (c). Longitude has values ranging from 0° ( Greenwich, U.K. ) to + 180° (eastly) and from 0° to -180° (westly).