A method of detecting when a navigable element previously determined to be closed is in an open state, the navigable element forming part of a network of navigable elements within a geographic area, the navigable elements being represented by segments of an electronic map, the method comprising: obtaining positional data relating to the movement of a plurality of devices along the navigable elements of the navigable network with respect to time; identifying a navigable element as being in a closed state based at least on the positional data and a first visit interval associated with the segment representing the navigable element, wherein said first visit interval is indicative of an expected time interval between consecutive devices being detected on the element when in an open state, wherein at least some of the segments of the electronic map are each associated with data indicative of a passability parameter for the segment, the passability parameter being indicative of the likelihood of the navigable element represented by the segment being closed, and wherein the value of the passability parameter varies according to a predefined function with respect to time such that the likelihood of the navigable element represented by the segment being closed increases with respect to time, the predefined function being based on the first visit interval, and wherein the identification of the navigable element as being in a closed state comprises: modifying the value of the passability parameter associated with the segment representing the navigable element, such that the likelihood of the navigable element being closed is decreased, when the positional data indicates that a device has been detected traversing the navigable element; and identifying the navigable element as being in a closed state when the value of the passability parameter associated with the segment representing the navigable element passes a predetermined closure threshold value; using the positional data to determine a second visit interval for the segment representing the navigable element, wherein said second visit interval is indicative of an average time interval between consecutive devices being detected on the element when it has been identified as being in the closed state; and changing the navigable element to be in an open state when a parameter based on the determined second visit interval for the segment representing the navigable element passes a predetermined opening threshold value. obtaining positional data relating to the movement of a plurality of devices along the navigable elements of the navigable network with respect to time; identifying a navigable element as being in a closed state based at least on the positional data and a first visit interval associated with the segment representing the navigable element, wherein said first visit interval is indicative of an expected time interval between consecutive devices being detected on the element when in an open state, wherein at least some of the segments of the electronic map are each associated with data indicative of a passability parameter for the segment, the passability parameter being indicative of the likelihood of the navigable element represented by the segment being closed, and wherein the value of the passability parameter varies according to a predefined function with respect to time such that the likelihood of the navigable element represented by the segment being closed increases with respect to time, the predefined function being based on the first visit interval, and wherein the identification of the navigable element as being in a closed state comprises: modifying the value of the passability parameter associated with the segment representing the navigable element, such that the likelihood of the navigable element being closed is decreased, when the positional data indicates that a device has been detected traversing the navigable element; and identifying the navigable element as being in a closed state when the value of the passability parameter associated with the segment representing the navigable element passes a predetermined closure threshold value; using the positional data to determine a second visit interval for the segment representing the navigable element, wherein said second visit interval is indicative of an average time interval between consecutive devices being detected on the element when it has been identified as being in the closed state; and changing the navigable element to be in an open state when a parameter based on the determined second visit interval for the segment representing the navigable element passes a predetermined opening threshold value.