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Geospatial Analysis with AutoCAD Map 3D, Part 2
18 Nov, 2009 By: Michael SchlosserFind patterns — and answers — in your data by creating subsets and identifying features and objects.
Geospatial queries are at the heart of geospatial analysis; they are used to retrieve a subset of objects or features by attribute, location, or both. Queries help create subsets of the data, identify objects and features based on specific criteria, and reveal patterns in the data. Queries have two primary components: attribute conditions (e.g., Zone= "Industrial") and/or geographic conditions (e.g., number of water meters within a specific area). Queries are used to answer questions such as:
- "How many municipalities are in the state of Georgia?"
- "What is the total length of 8-inch PVC water main within city boundaries?"
- "Where are all the land parcels that are zoned industrial?"
AutoCAD Map 3D software supports the ability to query both CAD data and feature data. CAD data is typified by geometric data such as points, lines, text, and other CAD entities stored in DWG files. Features, on the other hand, are spatial representations of real-world entities such as hydrants, power lines, and land parcels. Feature data is typically stored in geospatial files and databases including ESRI SHP files, SDF, Oracle, PostGIS, and ESRI ArcSDE managed databases, as well as other formats. This article focuses on the feature data query capabilities in AutoCAD Map 3D.
Feature Data Queries
For this example, we will query an ESRI SHP file containing land parcels to create a map that dispalys all parcels with land values less than $10,000 that are also touching a particular geographic region, as indicated by a user-specified rectangular window.
To query feature data, you must first connect to a geospatial data source containing the features to be queried. By connecting to a feature data source rather than relying on an import process, you can work with the feature data directly in its native format without first having to create a copy of the data.
In Display Manager, click Data > Connect to Data to reveal the Data Connect window.
In the left pane of the Data Connect window, select the data provider corresponding to the geospatial data source to be queried — in this example, it's Add SHP Connection. In the right pane, specify the connection parameters to the PARCELS.SHP file and click the Connect button.
Next, in the Add Data to Map section, under Schema, select the feature classes to include in the map. If the data source contains only a single feature class, as it does in this case, that feature class is selected automatically. To display all of the features without creating a query, click the Add to Map button.
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About the Author: Michael Schlosser
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