The elevation grid and lowland file are in a different coordinate system than the rest of the data. Thats not a problem as long as the coordinate system is defined for those datasets. Without this information, however, ArcMap cant do a geographic transformation and the data cant be displayed or overlaid with the other project data. While the coordinate system for the elevation grid is defined, when the lowland shapefile was created from the grid, the coordinate system information was not included. You need to define the coordinate system for the shapefile.
If you closed ArcCatalog at the end of Chapter 5,
Assembling the database, youll need to reopen it now.
Check the coordinate system information Before defining the coordinate system for the lowland shapefile, youll check the coordinate system definitions for the City data and for the elevation grid. Youll do this by examining the metadata for the datasets.
1. In ArcCatalog, navigate to the WaterProject geodatabase under the project folder in the Catalog tree.
2. Open the database to list its contents, then click the parks_polygon feature class.
This feature class, which you copied from the Citys GreenvalleyDB, is in the same coordinate system as the rest of the Citys data.
3. Click the Metadata tab.
4. Click the Spatial tab in the metadata panel.
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You can see that the coordinate system for the
parks_polygon feature class uses a Transverse_Mercator projection.
Metadata contains information about each dataset. Some of the information is assigned and maintained automatically by ArcGIS; other information you add interactively.
Metadata is invaluable when sharing datasets and for documenting GIS projects.
In this project youll use metadata to get information you need for several of the steps. Metadata lets you store a great deal of information about a dataset: source,
processing status, data quality, attribute values, and much more. For several of the datasets, weve provided some of the key information youll need for the project.
In an actual GIS project youd also use metadata to keep track of modifications you make to existing datasets and to document new datasets you create during the project.
Adding or updating the metadata for a dataset takes a little extra time, but it pays off if you need to reuse the dataset in
the future, share it with another department or organization, or reconstruct your processing steps.
Now check the coordinate system for the elevation grid.
5. Navigate to the State_share folder in the Catalog tree, open it, and click elevation.
6. Click the Spatial tab (when you select a new dataset, ArcCatalog defaults the metadata display to the Description tab).
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You can see that the elevation grid is in a coordinate system that uses a Lambert_Azimuthal_Equal_Area projection.
Finally, check the coordinate system information for the lowland shapefile.
7. In the State_share folder, click lowland.
8. Click the Spatial tab.
The metadata lists the bounding coordinates for the shapefile but doesnt list the coordinate system since it is unknown.
When you previewed the data in Chapter 5, Assembling the database, ArcMap was able to transform the elevation grid on the fly and display it with the other project data since the coordinate system was defined and stored with the grid. Because the coordinate system for the lowland shapefile is unknown, ArcMap was unable to transform it.
Define the coordinate system for the lowland shapefile
Presumably, the coordinate system for the lowland shapefile is the same as for the elevation grid since the shapefile was originally created from that grid. But you dont know for sure. Thoughtfully, the analyst at the Department of Transportation who sent you the data also included a spatial reference file that defines the coordinate system the department uses for all its data. Youll use the file state_dot.prj to define the coordinate system for the shapefile within ArcCatalog.
1. Right-click lowland in the Catalog tree and click Properties.
The Shapefile Properties dialog box appears.
2. Click the Fields tab.
The fields in the shapefiles attribute table are listed.
The Shape field contains the coordinate information for the shapefile.
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3. In the Field Name list, click the row containing Shape.
The properties for the Shape field are displayed below in the Field Properties list. You can see that the Spatial Reference property is listed as Unknown.
4. Click the button with the ellipses ( ) to the right of Spatial Reference.
The Spatial Reference Properties dialog box appears.
Youll be defining the coordinate system by selecting a predefined coordinate systemspecifically, the one contained in the state_dot.prj file that accompanied the elevation and lowland data.
5. Click Select.
5 3
4
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6. Navigate to the State_share folder under the project folder connection, click state_dot.prj, and click Add.
The name of the coordinate system appears in the Spatial Reference Properties dialog box, and the details are listed. You can see that theyre the same as for the elevation grid.
7. Click OK to close the Spatial Reference Properties dialog box.
The name of the coordinate system now appears in the Field Properties list.
8. Click OK to close the Shapefile Properties dialog box.
You can verify the new coordinate system in the metadata.
9. Click View and click Refresh, then click the Spatial tab.
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You can see that the coordinate system for the lowland shapefile is now defined.
With the coordinate system defined, the lowland shapefile should now display correctly with the other project data and can be used in overlay operations during the analysis.
You can check this in ArcMap.
10. Click the Launch ArcMap button on the toolbar.
11. In the startup dialog box, click wastewater data.mxd
and click OK (if the startup dialog box doesnt appear, click File on the ArcMap toolbar and click wastewater data.mxd).
Launch ArcMap
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The lowland layer now appears in the same geographic
space as the other project data. 12. Click lowland in the table of contents and drag it to the bottom so it displays beneath the elevation grid.
You can see the layer under the elevation grid and see that it does in fact encompass the lowest elevations in the City.
13. Close ArcMap. You wont be using this map again, so click No when prompted to save changes to the map.
Lowland shapefile
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