A network system determines dissimilarities between a digital map and trace data of a road network in an area as service providers and service requestors coordinate service using the road network in the area. To determine dissimilarities the network system can determine a suggested route, determine a predicted route, receive executed trace data, and compare the predicted route data to the executed trace data for the suggested route. The network system may aggregate trace data when determining a dissimilarity. The network system can quantify the differences between traces to determine dissimilarities. Quantifications can include, ratios, bounds, and scores. The network system can determine and alternate route if a dissimilarity indicates that the state of a road segment has changed (e.g., from “open” to “closed”). The network system can modify guidance instructions if a dissimilarity indicates that a guidance instruction is misleading.