Linear Referencing

Analysis of the relationship between pavement conditions and accidents in Pitt County, NC.

Problem and Objective

A linear referencing system is a spatial referencing method where points or segments along a linear element are dynamically located and described in terms of measurements from a fixed point along a road. The purpose of this analysis is to determine the spatial relationship between pavement conditions and accident events reported along the routes and roads of Pitt County. Furthermore, a customized ArcGIS pro interface will be developed to streamline this and any other similar process of linear referencing.

Analysis Procedures

Strategies: The strategies adopted for this analysis are explained as follows. I used ArcGIS Pro (Version 2.9) software. I used the following Modules/tools for the analysis: Select by Attribute tool, Identify Route Locations tool, Overlay Route Event Layer tool, and Make Route Event Layer tool. Data and data types – The data include (a) a file geodatabase of routes in Pitt County (b) Shapefiles of county and cities boundary (c) DBF tables of accidents and pavement events and (d) a downloaded custom Add-In tool called LRS tools. Data sources – GIS 520 Fall Semester, NCSU, and Texas Department of Transportation (GitHub).

Methods: Starting with the first part of the assignment, I created a new tab called Linear referencing under the Customized the Ribbon window from the Project tab (Option). I verified to see if the new tab is now on the ribbon. After locating the Linear referencing tab in the Customize the Ribbon window, I added three new groups to the tab and renamed them as follows: (a) Routes (b) Events, and (c) Add-In Tools. Next, I added the Calibrate Routes, Create Routes, and Locate Feature Along Route tools to the Routes group. I also added the Dissolve Route Events, Make Route Event Layer, Overlay Route Events, and Transform Route Events tools to the Events Group. After downloading and installing the LRSTools, I searched through All Commands and added the Identify Route Locations and Set From/To Measures tools to the Add-In Tools group. I added the three Roads-Routes features to the map and inspect their respective attribute tables. I used the Identify Route Locations tool to view the attribute information of Route 30000030 by clicking on it on the map. Upon adding the accident events table to the map, I used the Select by Attribute tool to select the number of accidents along Route 30000030. I made a route event (point) layer using the Some-Route feature class (Route Features) and the Accident table (Event Table) using their respective Route Identifier Field. Using the Select by Attribute tool, I selected the pavement events on Route 30000030 after adding the pavement table to the map. By clicking on the Show Selected Records, I was able to inspect the attributes of these selected pavement events and sort them in ascending order. Next, I made a route event (line) layer from this pavement table and Some Route features using the Make Route Event Layer tool. I exported all records in this feature as a standalone table into the file geodatabase using the Export Table tool. I added a new field to this table. Next, I used the Calculate Field tool to calculate the segment length using a query/expression. I selected the segment of pavement events along Route 30000030. With the current selection active, I used the select by attribute tool to select segments with ratings greater than 75. With this similar approach, I selected ratings less than or equal to 75. Next, using the Overlay Route Events tool, I created a table with records representing the intersection of the points events (Accident Route events) and line events (Pavement Route events) using their respective Route Identifiers and measure fields. I made a route event layer from this table along with the Some Routes feature class using the Make Route Event Layer tool where the event type is Point.

External links: Customize the ribbon options, Linear referencing data, Overlay Route Event

The workflow diagram of customizing ribbon and linear referencing

Result

The dots represent individual accidents on a specific pavement route event. The yellow dots are the accident events on routes rated 75 and below and the orange dots are the accident events on the routes rated above 76.

Application & Reflection

Problem Description: Different smaller (streams) tributaries make up a watershed. Additionally, a watershed could have one or more stream gauges on any of these smaller creeks/streams. Considering that stream gages measure and records the water level of streams, this analysis aims to show the relationship between the stream gradient and the sample of suspended sediments. Several factors influence the amount of sediment carried by a stream. This analysis will help inform a decision about the ability of the stream to carry sediments and any incidence of erosion or mass movement.

Data Needed: The data needed include (a) a shapefile of a county storm watershed (b) a dbf table file of stream segments serves by each gauge point with a column representing the stream slope of each segment (c) a dbf table of individual stream gages along the stream route with information of their respective current water level with suspended sample sediments (d) a line feature of county streams and creeks.

Link to suggested data: NC Stream Mapping Program

Analysis Procedures: Upon adding all data to the map, I will examine the attribute table of individual feature classes as well as the tables. Some stream gauges may not fall exactly on the stream, using the snapping tool, I will place these gauges in their respective locations on the stream. I will use the Identify Route Locations tool to view the attribute information of any stream by clicking on it on the map for a better understanding of the feature. Then, I will make a route event (point) layer using the stream shapefile (Route Features) and the stream gauge (Event Table) using their respective Route Identifier Fields. Next, I will make a route event (line) layer from the stream segments table and stream shapefile using the Make Route Event Layer tool. Next, using the Overlay Route Events tool, I created a table with records representing the intersection of the points events (Stream gauge) and line events (Stream segments) using their respective Route Identifiers and measure fields. I will make a route event layer from this table that will represent the gauge points and the stream segments served by the gauge points along the Stream Routes feature class using the Make Route Event Layer tool where the event type is Point. I will plot of water depth-sediment relationship as well as a plot of the stream gradient-sediment relationship using the chart tool. And finally, I will change the symbology of the stream segment based on its slope value while the value for the water level of individual stream gauges will be used to label them.

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