Lab9 of Geo520, Spring 2005

TA : Julie Hwang

Lab 9. Linear Referencing Systems

Objectives

The objectives of this lab are to introduce linear referencing systems, and to work with linear referencing systems in TransCAD.

 

Linear Referencing Systems

Rounded Rectangular Callout: Example of a point milepost layer Data on networks often store location information using a route identifier and a distance from a fixed point on the route. The distance from the fixed point is known as the milepost (or measures in some literatures).

Rounded Rectangular Callout: Example of a line milepost layer

Practice #1: Work with mileposts

______ Copy the directory H:\GEO520Lab\Lab9\Practice to your own space, and open the map SR5.map in your space.

______ Create a Network based on the selection set named SR5S. (use Network/paths-Create).

______ Create a Route System from the network you just created. Make sure you check Linear referencing under Options in the New Route System dialog box.

_____ Add a new route to Route System from the southernmost node to the northernmost node in the selection set named SR5S. (Use Route Systems – Editing Toolbox). Give the name “5” to a new route.

_____ Choose Route Systems – Route Query Toolbox when Route System is set to an active layer. This time you will see more buttons because you chose Linear referencing option which allows you to edit milepost values along the route. Check the milepost value using .

_____ Make Endpoints layer shown and move down the layer so that it can be shown over the route in a map (use ). You may want to change the style of the layer to make it pronounced.

_____ Click  when the active layer is the Route System. Check the radiobox Show Mileposts on Routes under Route Settings.

Milepost values are not necessarily based on the actual elapsed distance along the route. This can happen when the route passes through multiple jurisdictions. You will be editing milepost values in reference to the table provided for you.

_____ Open RTRAT.dbf in the directory you copied. This table contains the information on new milepost values along the route you just added. Look into two fields named BEGMPT and ENDMPT. The location of each segment is stored using these two fields. For example, the first segment starts from 0.155 and ends at 2.217. Note the starting milepost value is not 0.

_____ Click  in the Route System Query Toolbox when the Route System is an active layer and route 5 is chosen in the drop-down list.

_____ Click on the starting node and then type in 0.155 (this is the BEGMPT of the first record in the RTRAT.dbf) in the Milepost inputbox. Do the same for the location of the next nodes. The ending nodes should have the value of ENDMPT of the last records. Whenever you edit the milepost values, make sure you commit the milepost values using the green light button.

_____ Choose Window-Refresh. This will display the new milepost values in the map as shown below.

_____ Keep these working files to save time for the assignment.

Practice #2 Create milepost layers

We have learned how to geocode data stored in street address or geographic coordinates. In this practice, you will be geocoding data based on a linear referencing system. Two kinds of milepost layers will be created with this; Point layer (e.g. accident) requires “a milepoint in which route?”. Line layer (e.g. traffic volume) requires “the start AND end milepoints in which route?”.

______ Open fars01_5.dbf and hpms01_5.dbf. The first table contains the point location of fatal traffic crashes in milepost values. The second table contains the line location of different segments in milepost values.

______ Take a moment how different the way the location information is stored. Scroll all the way to the right in fars01_5.dbf, and find the field MILEPOINT and Route_ID. It says each accident occurs in the milepoint value in the route. In hpms01_5.dbf, find the fields BEGIN_LRS, END_LRS, and Route_ID. It says each segment is located from BEGIN_LRS to END_LRS along the route.

______ Make the Route System an active layer. Choose Route Systems – Linear Referencing – Attach….

______ Choose fars01_5 from the Dataview drop-down list, which will automatically give fars01_5 Layer as a name, and check the optionbox Point layer. You are attaching a milepost table (fars01_5.dbf) to Route System through Route Identifier (ROUTE_ID) and milepost values (MILEPOINT).

______ Make the fars01_5 layer active, and change the style such that the layer can look pronounced. This is how you geocode the point event data stored in mileposts along the route.

______ Make the Route System an active layer. Choose Route Systems – Linear Referencing – Attach….  

______ Choose hpms01_5 from the Dataview drop-down list, which will automatically give hpms01_5 Layer as a name, and check the optionbox Line layer. You are attaching a milepost table (hpms01_5.dbf) to Route System through Route Identifier (ROUTE_ID) and milepost values (BEGIN_LRS to END_LRS).

______ Make a scaled-symbol map of hpms01_5 Layer using the attribute AADT (Average Annual Daily Traffic).

______ See if there is any correlation between traffic crashes and traffic volume.

Practice #3 Create strip charts

Strip charts are a set of graphs that show the characteristics of a route and how they vary along the length of the route.

______ Make the Route System active, then choose Route Systems – Linear Referencing – Strip Chart….

______ Choose 5 from the Route drop-down list, and choose attributes [hpms01_5 Layer].AADT, [hpms01_5 Layer].THROUGH_LA, and [fars01_5 Layer].MILEPOINT (use ctrl key). Click OK.

It seems that accidents are concentrated in the segments between 1 and 10 miles from the reference points along the routes.

Practice #4 Convert a milepost layer to a geographic file

______ Choose Tools-Export while you choose the milepost layer you want to convert in the layer drop-down list.

______ Choose the features to export, a file format, and data field to convert the milepost layer into a geographic file.

Practice #5 Create intersection diagrams

______ Choose the layer erierts from the layer drop-down list.

______ Choose  (intersection diagram) in the toolbox.

______ Click on any intersection (eg. Clinton Rd/Transit Rd) of the layer erierts.

______ In the Intersection Diagram dialog box, choose LANES for the Forward Flow drop-down list, and LANES for the Reverse Flow drop-down list.

Intersection diagram will be displayed by taking into account the directionality of road segments and their attributes you set in the flow drop-down list. If you have the information of traffic flow that varies by the direction of the road segment, you can specify them as well

Practice #6 Create prism maps

______ Open BOS_HWY.map in the Tutorial folder.

______ Make County an active layer.

______ Choose Maps-Prism Maps.

______ Choose [Sales Per Client] for the Field drop-down list under Data when the Prism Map Properties dialog box pops up. Click OK.

______ Play with prism map using 3D control toolbox such as Rotate, Zoom, and Pan.

Practice #7 Create charts from tabulations

______ Open fars9601.dbf from the practice folder. The file contains the fatal crashes in New York states between 1996 and 2001. You may want to know how the accident frequency varies by month or year.

______ Choose Statistics from the Procedures menu if Statistics menu is not shown.

______ Choose Statistics-Tabulations. Choose Months for Field1 drop-down list, List of Values for Method drop-down list, 13 for the # Classes drop-down list. This will create the tabulations of accident frequencies by month.

______ Give any name when the Save As dialog box pops up.

______ Look into the matrix. Which month shows the highest rate of fatal traffic crashes? Choose all cells under the Count column.

______ Choose , then choose Chart in the New File dialog box.

______ Make sure Selected Cells is checked in the Matrix C     hart data dialog box.

______ Choose vertical bar for the chart type, and check the 3D and Labels under the Options.

______ In the resulting chart, double-click on the x axis. In the Chart Properties dialog box, choose Axis Settings tab, and type in 400 for the From input box. Click OK.

______ Do the same for the field YEARS. Create the bar chart showing how accident frequency varies by year.

Assignments (due at the beginning of next lab):

In this assignment, you will be doing the same thing as you do in the practices. Use the data set provided in H:\GEO520Lab\Lab9\Assignment. fars00_5.dbf is the linearly referenced fatal traffic crashes in year 2000 at the Route 5 (you created in the practice #1). hpms00_5.dbf contains the characteristics of the Route 5 by segments in year 2000.

1.      Create two milepost layers: (1) Point layer: accident layer from fars00_5.dbf (2) Line layer: highway segment layer from hpms00_5

2.      Create the chart showing how hazmat accident frequency varies by month using hmirs02.dbf

Submit a map showing two milepost layers where accident location and AADT for each road segment are displayed (practice #2). Submit a strip chart that shows AADT, Lane, and accident location (practice #3). Submit the chart of hazmat accident frequency by month (practice #7).

The data provided in this lab can be downloaded in BTS website, particularly in the subject under Highway. Use the following link for download and further information: http://www.transtats.bts.gov/Databases.asp?Mode_ID=3&Mode_Desc=Highway&Subject_ID2=0