Linear referencing allows you to find a location along a route. For example, you can find where an accident occurred, if you know the mile post or other measured location and the highway. It is often harder to find a route location on a paper map because route measures are typically not shown. In ArcMap, finding a location on a route is simple.

To find a location by linear referencing, click the Find button on the ArcMap Tools toolbar. Click the Route Locations tab and use the Route Reference drop-down list to select the route feature class. In this example it is called "routes_new."

If you have set the Route Identifier field in the route layer's properties in ArcMap, the Route Identifier field will already be listed in the Route Identifier drop-down list. If you haven't, you can select the field that contains the route identifier values.

Click Load Routes to get a list of the routes in the route feature class, then click the Route drop-down list and click the route for which you want to find a measured location.

Route identifier numbers are often a combination of numbers and should be designed to have no political, social, or economic meaning, so they will not change over time.

Type a measured distance in the Location box to find the position of this location along the route you selected, and click Find.

You can right-click the resulting route locations to flash the route or route location, zoom to the route or location, draw a graphic or label the location, or get more information about the route feature.

Route measure values are typically expected to follow certain rules. For example, they should usually increase steadily along the route, and all of the parts of the route should usually have meassure values.

You can find places where route measures do not behave as expected. These are often the result of digitizing or attribute entry errors in the data from which the routes were built. Such places are called route measure anomalies, and they can be fixed with the route editing tools in ArcMap.

To view route measure anomalies, right-click the routes layer in the table of contents and click Properties. Click the Routes tab and check the box to "Show where measures do not." You can choose between finding where they do not increase, and finding places where measures do not increase with the digitized direction of the route features. Optionally, click the Line Symbol button and select a line or marker symbol you want the anomalies drawn with.

Route measure anomalies can be fixed with ArcMap route editing tools.