March 14, 2006

Domain Constraints from CAD Data

My two year old has reached a developmental mile stone; in the last two days she has learned how to climb out of her crib, overcome the child safety doorknob locks and manipulate the large front door. She used these three skills in combination with her existing ability (to use most any container as a stepping stool) to make a break for it yesterday down the sidewalk!

Today’s obvious topic is domain CONSTRAINTS! My daughter’s domain constraints have to be a safe area in her home free from the perils of automobile traffic, harmful chemicals and other normally harmless everyday objects that when placed in the hands of a two year old become life threatening.

In ArcGIS attribute domain constraints limit the valid values in a column to a discrete set or a range of values. One can use a table to help set the domain constraints in ArcGIS for the valid values in a column.

Today’s suggestion is to use the ArcView FREQENCY geoprocessing tool on CAD properties to get a table that I can use as the basis for my ArcGIS domain constraints. This is common when loading new CAD data into an ArcGIS feature class. If I have lots of AutoCAD blocks with ATTRIBUTES or Microstation TAGS and want to find all the values used in the drawing for a particular attribute TAG I can use the FREQUENCY tool to build a table of all the unique occurrences of a particular value. The resulting table will be the unique occurrences and their frequency (c0unt). Even if the values are coded as symbolic variances like COLOR or LINESTYLE at least I will know how many different kinds of features or values I am dealing with in any given CAD dataset.

As a secondary benefit to running the FREQENCY tool I may find values that I consider to be invalid for that attribute domain. In this way the FREQUENCY tool is useful for many types of quality control tasks.


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