A method of generating a database for a navigation device, said method comprising the following steps performed before the database is deployed to the navigation device for use in generating perspective views: retrieving a plurality of two-dimensional road vectors (66; 88, 89) from a map database, each one of said two-dimensional road vectors (66; 88, 89) defining a road segment of a road network; retrieving digital terrain model data defining a three-dimensional surface; for each two-dimensional road vector (66; 88, 89) of said retrieved plurality of two-dimensional road vectors (66; 88, 89): establishing a projection (72, 73) of said two-dimensional road vector (66; 88, 89) onto said three-dimensional surface along a pre-defined projection direction; determining at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) based on said established projection (72, 73), said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) including height information for points located on the at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138); and storing said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138) in said database; and generating modified digital terrain model data based on said digital terrain model data and based on said determined at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) to ensure a seamless transition between road segments and surrounding terrain when a three-dimensional map is output by the navigation device, wherein said modified digital terrain model data are stored in said database before said database is deployed to said navigation device; wherein generating said modified digital terrain model data includes: determining, for plural of said determined three-dimensional road vectors (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138), a triangular facet in which the respective three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) extends and which has an edge (101, 102) normal to both the three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) and said projection direction. retrieving a plurality of two-dimensional road vectors (66; 88, 89) from a map database, each one of said two-dimensional road vectors (66; 88, 89) defining a road segment of a road network; retrieving digital terrain model data defining a three-dimensional surface; for each two-dimensional road vector (66; 88, 89) of said retrieved plurality of two-dimensional road vectors (66; 88, 89): establishing a projection (72, 73) of said two-dimensional road vector (66; 88, 89) onto said three-dimensional surface along a pre-defined projection direction; determining at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) based on said established projection (72, 73), said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) including height information for points located on the at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138); and storing said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138) in said database; and establishing a projection (72, 73) of said two-dimensional road vector (66; 88, 89) onto said three-dimensional surface along a pre-defined projection direction; determining at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) based on said established projection (72, 73), said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) including height information for points located on the at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138); and storing said at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118,135-138) in said database; and generating modified digital terrain model data based on said digital terrain model data and based on said determined at least one three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) to ensure a seamless transition between road segments and surrounding terrain when a three-dimensional map is output by the navigation device, wherein said modified digital terrain model data are stored in said database before said database is deployed to said navigation device; wherein generating said modified digital terrain model data includes: determining, for plural of said determined three-dimensional road vectors (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138), a triangular facet in which the respective three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) extends and which has an edge (101, 102) normal to both the three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) and said projection direction. determining, for plural of said determined three-dimensional road vectors (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138), a triangular facet in which the respective three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) extends and which has an edge (101, 102) normal to both the three-dimensional road vector (78, 79; 81-83; 94, 95, 98, 99; 115-118, 135-138) and said projection direction.