Thursday, March 24, 2005

Thematic Queries in GTViewer

GTViewer offers a very powerful tool called Thematic Queries (sometimes called Highlight Queries). This posting will describe what this feature does and what it can do for you.

Locate Queries are the type of query most GTViewer users are familiar with. These queries allow the user to key in a search criteria, show a list of matching results, and then graphically locate on a single item in the list.

A Thematic Query is very different. It allows the user to key in a search criteria, but instead of showing the tabular results, it highlights all of the features matching the specified search criteria thereby creating a Theme. The user can specify the color and weight of the Theme. Multiple Thematic Query results can be displayed at the same time and the Emphasize Session Graphic mode can be used to enhance the display of a Theme. The Thematic Query is easier to describe with pictures than with words. The first example below shows a Circuit highlighted in Red. This Thematic Query let the user select from a list of Circuit ID, then let the user pick the color and weight properties.




The following picture shows 3 circuits highlighted in Red, Blue, and Magenta.



The Thematic results are highlighted elements. This fact has some implicit meaning that is worth going over. Besides seeing the visual results of a Thematic Query, you can also:

  • Count Thematic Query Results in polygons (with the Feature Counting command)
  • Convert Thematic Query Results to Session Graphics (with Tools/Convert Highlighted Elements to Session Graphics)
  • Reviewed Results as if they were regular features in the graphics (the original element does not have to be displayed)
  • Print Thematic Query Results
  • Exported Thematic Query Results (to a .gtg or DGN file).

Thematic Queries have a variety of uses. One of the more innovative uses I have seen came from a customer who was Highlighting all elements that had a specific Tax Code property. First, the Thematic results were used to verify that the Tax Code properties were correct. This task is easily done when you can visually see the results as a whole. Second, the Count command was used to create two different reports. For the first report, session graphics shapes were drawn around features that were not in the appropriate Tax Boundary. The Thematic results in the polygons were counted and a report created with the features with the wrong Tax Code property. For the second report, the Tax Boundary shapes were used to count all of the highlighted features to produce a report of all features in the Tax Boundary. The Count reports show the total lengths of linear elements automatically.

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