A method of detecting the closure and/or opening of a navigable element forming part of a network of navigable elements within a geographic area. A passability parameter is associated with each segment of an electronic map representing the navigable network and indicates a likelihood of closure of the element represented by the segment. The value of the passability parameter decays over time. When a device is detected on the element represented by the segment, the passability parameter is increased, and when a closure report is received relating to the segment, the parameter is decreased. In one set of embodiments, when the passability parameter decreases below a first threshold value, the element represented by the segment is determined to be potentially closed. In another set of embodiments, when the passability parameter increases above a second threshold value, the closed element represented by the segment is determined to be opened.