A computer-implemented method of determining a geographic position of a feature identified along a route travelled by a vehicle, the method comprising: receiving a set of route data obtained as the vehicle travels along the route, comprising: a first route trajectory of the vehicle measured in a relative coordinate system; a second route trajectory of the vehicle measured in a geographic coordinate system; and a plurality of features having a position measured in the relative coordinate system; determining a spatial relationship between the relative coordinate system and the geographic coordinate system, wherein the spatial relationship is determined in dependence on a part of the first route trajectory and a part of the second route trajectory, wherein the part of the first route trajectory and the part of the second route trajectory are both measured between a first time and a second time; receiving known topographic data comprising one or more known topographic features having a known position measured in the geographic coordinate system; matching one or more features in the route data to one or more of the known topographic features in dependence on the determined spatial relationship to determine at least two tie points (TP1, TP2) between the relative coordinate system and the geographic coordinate system; and transforming a position of one or more unmatched features in the route data from the relative coordinate system to the geographic coordinate system in dependence on the at least two tie points (TP1, TP2) to thereby determine a geographic position of the one or more unmatched features. receiving a set of route data obtained as the vehicle travels along the route, comprising: a first route trajectory of the vehicle measured in a relative coordinate system; a second route trajectory of the vehicle measured in a geographic coordinate system; and a plurality of features having a position measured in the relative coordinate system; a first route trajectory of the vehicle measured in a relative coordinate system; a second route trajectory of the vehicle measured in a geographic coordinate system; and a plurality of features having a position measured in the relative coordinate system; determining a spatial relationship between the relative coordinate system and the geographic coordinate system, wherein the spatial relationship is determined in dependence on a part of the first route trajectory and a part of the second route trajectory, wherein the part of the first route trajectory and the part of the second route trajectory are both measured between a first time and a second time; receiving known topographic data comprising one or more known topographic features having a known position measured in the geographic coordinate system; matching one or more features in the route data to one or more of the known topographic features in dependence on the determined spatial relationship to determine at least two tie points (TP1, TP2) between the relative coordinate system and the geographic coordinate system; and transforming a position of one or more unmatched features in the route data from the relative coordinate system to the geographic coordinate system in dependence on the at least two tie points (TP1, TP2) to thereby determine a geographic position of the one or more unmatched features.