A method of generating a 2D map for image aided navigation, the method comprising: detecting one or more edges of objects shown in one or more terrain ortho-images ; and obtaining a compressed edge map representation of the one or more edges , the compressed edge map representation obtained by a method comprising: fitting one or more line segments to the one or more edges , wherein fitting the one or more line segments to the one or more edges comprises: dividing the one or more terrain ortho-images into multiple pixel blocks of a uniform size; and fitting the one or more line segments to edge pixels inside of each pixel block; calculating one or more coefficients based on the fitted one or more line segments , wherein calculating the one or more coefficients comprises determining coordinates of endpoints for the one or more line segments where the one or more line segments intersect a boundary of the pixel blocks; and storing the one or more coefficients in a database for use in generating the edge map representation for image aided navigation , wherein storing the one or more coefficients comprises storing the coordinates of the endpoints for the one or more line segments. detecting one or more edges of objects shown in one or more terrain ortho-images ; and obtaining a compressed edge map representation of the one or more edges , the compressed edge map representation obtained by a method comprising: fitting one or more line segments to the one or more edges , wherein fitting the one or more line segments to the one or more edges comprises: dividing the one or more terrain ortho-images into multiple pixel blocks of a uniform size; and fitting the one or more line segments to edge pixels inside of each pixel block; calculating one or more coefficients based on the fitted one or more line segments , wherein calculating the one or more coefficients comprises determining coordinates of endpoints for the one or more line segments where the one or more line segments intersect a boundary of the pixel blocks; and storing the one or more coefficients in a database for use in generating the edge map representation for image aided navigation , wherein storing the one or more coefficients comprises storing the coordinates of the endpoints for the one or more line segments. fitting one or more line segments to the one or more edges , wherein fitting the one or more line segments to the one or more edges comprises: dividing the one or more terrain ortho-images into multiple pixel blocks of a uniform size; and fitting the one or more line segments to edge pixels inside of each pixel block; dividing the one or more terrain ortho-images into multiple pixel blocks of a uniform size; and fitting the one or more line segments to edge pixels inside of each pixel block; calculating one or more coefficients based on the fitted one or more line segments , wherein calculating the one or more coefficients comprises determining coordinates of endpoints for the one or more line segments where the one or more line segments intersect a boundary of the pixel blocks; and storing the one or more coefficients in a database for use in generating the edge map representation for image aided navigation , wherein storing the one or more coefficients comprises storing the coordinates of the endpoints for the one or more line segments. <EOS>