summer project

Geographic Information Systems
WORKSHOP - 1997

Prepared by: Kimberly Farwell - University of Texas at Dallas

The GIS Workshop consists of an independent project that is designed by the student. The workshop is usually the last in the GIS series of classes, and gives the student a chance to demonstrate their competence in using the tools of GIS. Workshop projects are often created to apply to the student's field of interest.

PROJECT INDEX:

PROJECT OBJECTIVE
SETUP
PROJECT AML
ARCEDIT TRANSFER
TRANSFER COMMANDS
MAPS

PROJECT OBJECTIVE:

Create a methodology for conflating the North Texas Council of Governments - Regional Base Map street attribute file to the North Central Texas - GIS Consortium street centerline file for the area covering the City of Mesquite. Completion of this project will result in a more accurate coverage overall.

Problem with objective: As so often happens with "the best laid plans" a major problem quickly became clear.

In order for conflation techniques to be successful you must be able to do feature matching - this means that you must have coverages that are a reasonable spatial match. In the case of the coverages being used, the features between the coverages have a very poor spatial relationship. The editing effort that would be required to prepare the coverages for conflation would have been even more time consuming than the alternate plan that was chosen. . . TRANSFER.

SETUP

  1. Using ARC/INFO, go into the arc attribute tables (.aat) of both coverages being used. Using the ITEMS command, review the template of each data file - template displays the data file name, the number of defined items, and the characteristics of each item. Make sure that all items that are going to be transferred in both files match exactly.

  2. Write an AML program to automate as much of the setup as possible. In addition to setting the map extent, editfeature, drawenvironment, backenvironment, backsymbolitems, transferfeatures, and transferitems, the AML should set the North Texas Council of Government's base map as the backcoverage (also specify a different color - I used blue), and the North Texas GIS Consortium's street centerline map as the edit coverage. The result is a map with the base map in blue overlayed with the street centerline map in white.

  3. Other helpfull additions for AML

    • Set the editsymbol so that the arc you are transferring at the time is displayed in a different color to cut down on any confusion that can arise when arcs are very close together.

      Example: editsymbol 0 green

      this command will change the selected arc from white to green for the duration of the transfer

    • In order to know which arcs have been transferred and which have not, it is best to select a transferitem that you know the value of, and calculate its symbol to be a very different color.

      Example: select TIGERID ne 0 and calculate $symbol = 13

      By setting select to TIGERID not equal to zero, and calculate symbol to hot pink, when I re-run the AML, all arcs that have been assigned a TIGERID (and therefore have already been transferred) will show up in a hot pink color.

To view AML used for this portion of the project go to PROJECT AML

PROJECT AML

display 9999
&term 9999
mape /mesquite1
editcover /mesq_rds1 arc
editfeature arc
drawenvironment arc node
transfercoverage /mesquite1
backcoverage /mesquite1 4
backenvironment arc node
backsymbolitem /mesquite1 arc
transferfeature arc
transferitems COGID TIGERID GDTID NAMEID PRE-DIR SUF-DIR ~ L-ADD.FROM L-ADD.TO R-ADD.FROM R-ADD.TO STRT-NAME STRT-TYPE
draw
editsymbol 0 green
select TIGERID ne 0
calculate $symbol = 13

ARCEDIT TRANSFER

In order to maintain database integrity, it is extremely important to first make a copy of your most recent coverage and do the editing process on your copy!

The actual transfer of attributes was done in ARCEDIT. As a graphics and database editor, ARCEDIT commands establish both the conditions and the environment in which spatial errors are corrected. ARCEDIT uses a four step feature-oriented editing process that:

specifies coverage containing features to be edited (editcover /mesq_rds1 arc)
specifies the feature class to be edited (drawenvironment arc node)
selects specific features within edit feature class to be edited (editfeature arc)
edits the selected features (transfer commands)

The actual transfer process is done while still in ARCEDIT:

AE:transfer (type in the transfer command)
-select transfer coverage arc with the (1) button on mouse
-select new coverage arc with the (2) button on mouse
-after a few transfers, click the (3) button on mouse to stop transferring and type in the SAVE command
-begin process again

This process will seem like a "point and click" operation until you come across an area where two source arcs exist where a target area has only one (or vise-versa). This is corrected by "splitting" the lacking arc in order to be able to match it to the transfer coverage. (Examples of split taken from ARC/INFO online help)


Select an arc (red line) and split it near the node in the old coverage (blue dashes).

AE: select (point to feature to select)
AE: split (point to where arc should be split)
AE: save



Now use the transfer command to copy attributes from the two source arcs to the two target arcs


The split that was just created appears as a red square.

AE: transfer
-select a source arc (blue dash) by clicking the (1) button
-select a target arc (red line) by clicking the (2) button.

Repeat for the next arc and remember to save.


MAPS