LINEAR REFERENCING
Problem
When a single linear feature has multiple attributes that each measure and overlap in different ways, it can become quite complicated as each new combination of attributes would need to be represented by a new feature. Linear referencing can overcome this issue by enabling association of multiple different attributes along a linear feature based on its measured location on that line. As an example, I need to use linear routes data in association with data on pavement quality and sites of automobile accidents to determine if the state of the roads impacts the number of accidents that occur on a given segment of road.
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Analysis Procedures
For this analysis, I plan to use the linear referencing tools available in ArcMap. I will use several data sets from Pitt County, NC that were provided for the GIS 520 students. This data includes road, route, county and city boundary layers, as well as tables of accident locations and various pavement attributes. I began this analysis by inspecting the different route layers and tables, along with their attribute tables. I determined that the “ROUTE1” column was a common attribute among the route layer and the data tables, so this attribute was used for linear referencing this data. I used the “Make Route Event Layer” tool to create a layer of points representing accidents along the routes, and another layer with pavement attributes referenced as linear segments along the routes. These two layers were then used in conjunction to create a new layer using the “Overlay Route Events” tool. The resulting layer displayed points that corresponded to accidents with the attributes of the pavement on which the accident occurred. The resulting data was used to calculate the number of accidents per mile along this specific stretch of road when the pavement had a rating of 75 or lower compared to that of accidents occurring on pavements with ratings higher than 75.
Figure 1. Diagram of methods.
Results
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Figure 2. Map of accident events.
Figure 3. Accidents based on pavement quality.
Application & Reflection
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Problem Description: Being able to compare multiple attributes based on a linear feature could be useful for a number of analyses. For instance, one could analyze the number of car accidents involving pedestrians based on the speed limit along each segment of road.
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Data Needed: To do this analysis, you would need roads data in the form of a route layer, speed limit data, and pedestrian accident data.
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Analysis Procedures: By linearly referencing these data to the roads, you could determine if there are areas in which the speed limit might be too high due to higher concentrations of pedestrian accidents. This would enable better city planning and help to reduce accidents.