Designing a linear referencing system in your geodatabase

The steps for designing a linear referencing system in your geodatabase involve a few key tasks:

1. Identify the reference line feature classes on which you want to locate events through measurements. The term reference simply refers to the line features whose geometry you want to locate points and line segments on. This is typically a base set of feature representations for roads, streams, pipelines, and so forth. This will most often be an existing key feature layer in your geodatabase.
2. Next, identify the events that you want to locate on your linear feature network including their system of measurements. These will be used to define a series of event tables. Many times, event tables already exist in your organization.

   Event tables can include various assets along your line features. For example:

   • Stream gauges along a river network located using river miles
   • Pavement type along highways located using miles from county boundary or highway interchanges
   • Locations of traffic signs along highways recorded using miles from county boundary or highway interchanges
   • Pipeline material type recorded along a pipe in meters or feet
   • Sediment type within a river reach recorded using river miles
   Event tables may also record the network condition or status. For example:
   • Road pavement condition measured by sensors and located using miles from county boundary or highway interchanges
   • Sewer condition along segments measured by sensors and located in meters or feet
   Tables to be located can also include events such as accident locations, weather conditions, and pipe damage.The key aspect of these event datasets is to define how the route features are to be identified (for example, using names or your organization's convention for route identification) as well as what the measurement system is for locating the events along the line network. The route ID will be set from the identification information, and the measurement system will be used to define your m-coordinates on your route feature class.

3. Identify how many route feature classes you will need. You'll need one for each measurement system. See Supporting multiple measurement systems for the same route features below.
4. Define the m-coordinate properties for each measurement system. You'll need to define your m-units of measure and the m-resolution and m-tolerance to be used when you create your new route feature class. Typically, you'll want to use the default m-tolerance value.
5. If you have more than one measurement system and, thus, more than one route feature class, organize these into a common feature dataset in the geodatabase.
6. Optionally, define a topology to integrate the individual route feature classes in your feature dataset.
7. Test and refine your design using a file or personal geodatabase.

Supporting multiple measurement systems for the same route features

Many departments will collect event data using the route measurement system that best suits their needs. You will likely encounter situations in which your event data will be recorded using more than a single system of measurements along the same linear route network.

For example, within a state department of transportation (DOT), the safety department might collect accident location events using a reference marker system of measurement, while the maintenance department might collect pavement quality information using a milepost system of measurement. You can readily support this in ArcGIS.

In ArcGIS, each route feature class can only store one system of measurement. To support multiple measurement systems, you'll need one route feature class for each measurement system.

In the geodatabase, organize multiple route feature classes, each having their own measurement systems, in a common feature dataset. Each route feature class can be created from a common set of reference lines (such as the reference streets). Essentially, you are copying the feature geometry to multiple feature classes and setting a unique measurement system for the m-values within each feature class.

Optional but highly recommended: You can use a topology to ensure the spatial integrity of the line features in each individual feature class. You'll want to ensure that each feature is coincident with and shares the same x,y,z coordinate locations for its corresponding features in the other route feature classes.

In the example below, a common set of linework, called the ReferenceLine feature class, is used as the source for the line geometry in all three route feature classes—one for reference marker measurements, one for mileposts, and a third for off-state-road routes. All these feature classes participate in a topology named R1Route_Topology.

Adding a topology to the feature dataset helps to ensure that events located with each route feature class will be coincident along one common set of road features.

We recommend using topology to ensure that the individual route feature classes are integrated and share coincident geometry according to data integrity rules that you define. The ability to manage these feature classes in an integrated fashion is critical.

Learn more about topology in ArcGIS

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