Implementing a geodatabase for local government

In an effort to centralize spatial data access and streamline city operations, the city of Rome in southern California (fictional city) is in the early stages of migrating its current GIS and CAD datasets to the geodatabase data model. After the data is stored in a geodatabase system, various city departments will be able to more easily share common data. This will cut the city's costs on managing and maintaining duplicate spatial datasets for each department.

Many departments want to participate in the geodatabase project. The city plans to centralize storage of spatial data and will eventually reduce the costs of maintaining it.

For its pilot project, the city is creating a personal geodatabase that will store some data from the Public Works, Planning, and Water departments, the city's largest GIS users. In later phases, the city plans to migrate to an enterprise system and will probably select Microsoft SQL Server as their database as some departments are already using SQL Server.

Sue, a GIS consultant from OMH Inc., is working on the pilot project for the city. To create the pilot geodatabase, one of the first issues she must deal with is defining the spatial reference of the datasets that will be stored in it.

For the spatial reference she needs to:

· Select an appropriate coordinate system

· Review the default spatial domain generated by ArcGIS

· Adjust the default spatial domain as needed

When deciding which coordinate system to use for the various feature classes in the geodatabase, Sue first investigated which one was being used for most of the existing data. Because the city has a limited geographic extent, selecting the NAD_1983_UTM_Zone 11N coordinate system for all feature datasets and standalone feature classes is appropriate. For a continental or global extent, data would have to be organized around a series of UTM zones.

For this geodatabase, the geographic extent of the different data layers is similar but there is some growth planned around the southeastern city boundary, which will need to be factored in within two to three months. Sue checks the default domain values that are created when she imports the shapefile with the largest data extent. The default spatial extent is large enough to accommodate the planned growth. The precision is also more than adequate to support the data. This spatial reference will be used for all feature datasets and feature classes.

Most of the city's non-CAD data are in coverage format and the coordinates are stored with double precision. When the coverages are converted to geodatabase feature classes, the coordinates will be stored in geodatabase precision. Some ArcView® shapefile data will also be converted to geodatabase features. The transition from double precision to geodatabase precision will result in a small change in precision, but will still be accurate.

The city's spatial datasets were collected at a scale of 1:1,200 and adhere to the National Map Accuracy Standards. Sue is using a precision of 1 foot for the water system data because it is important to get the exact location of the fire hydrants and water valves for maintenance and emergency response workers. She is organizing this data in a feature dataset called Water.

At a scale of 1:1,200, the city's roads and parcel data must have a horizontal accuracy of ±4 feet. Sue is creating separate feature datasets for Roads and Parcels.

A view of the city's pilot geodatabase in ArcCatalog.

Sue has scheduled some time for developing the metadata for each feature dataset and feature class. This information will help users when they access the data. For example, information on the coordinate system will help users know whether they can display other data with a particular feature class.

In ArcCatalog, you can review the metadata for a feature class to get important information about the data, including its coordinate system.

Now that she's determined the spatial reference for all the datasets that will be stored in the pilot geodatabase, Sue turns her attention to the data migration plan. Public Works has many CAD drawings that it wants to include in the project. ArcGIS provides an Import from CAD tool that converts CAD data to geodatabase feature classes. CAD text is converted to a point feature class. Parametric curve information is retained on the CAD features as it is converted to the geodatabase. CAD geometric properties and block and cell attributes can also be retained during the conversion.

For the city's pilot project, Sue's most important task is to populate the geodatabase and make sure there are no problems. For the remaining time of the pilot project, Sue will implement additional functionality of the geodatabase. If I get my act together, then you will see how the city's geodatabase project progresses in the remaining lectures of this course.