The next task is to project the river shapefile into the same coordinate system as the data in the Citys GreenvalleyDB geodatabase. According to your colleague at the County Water Resources Department, the river shapefile is in geographic coordinates (latitude and longitude). The rest of the data in the Citys database is in the Transverse
Mercator coordinate system, which is a projected coordinate system. As long as a dataset is in geographic coordinates, ArcMap can transform it on the fly to display and overlay it with the other data (as you saw in the last chapter).
However, the river data will eventually be placed into the Citys GreenvalleyDB database, so youll want to project it into the same coordinate system as the rest of the Citys data to be consistent.
Projecting the shapefile is a two-step process: first youll define the coordinate system for the shapefile; then youll define the output coordinate system and project the file.
Youll do both of these tasks in ArcToolbox. ArcToolbox contains a number of data management and conversion tools and wizards.
Define the coordinate system for the river shapefile
1. In ArcCatalog, click the Launch ArcToolbox button on the toolbar.
The ArcToolbox window appears.
2. Double-click Data Management Tools in the
ArcToolbox tree; click Projections, then double-click Define Projection Wizard. (If you are using ArcInfo you will see additional tools not shown here.)
The first screen for the wizard appears.
You defined the coordinate system for the lowland shapefile using the Properties dialog box in ArcCatalog.
The ArcToolbox Wizard provides an alternate way of defining a coordinate system.
Launch ArcToolbox
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3. Click the Browse button and navigate to the County_share folder under the project folder.
4. Click river.shp and click Add.
The wizard lists the shapefile. The coordinate system is listed as GCS_Assumed_Geographic_1. ArcGIS attempts to determine the shapefiles coordinate system based on the datasets coordinate values. In this case, ArcGIS has determined that the shapefile is in geographic coordinates
(latitudelongitude); however, you need to explicitly define the geographic coordinate system before you can project the data.
5. Click Next and click Select Coordinate System.
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There are three ways of defining a coordinate system: using a predefined coordinate system stored as a .prj file,
matching the coordinate system of an existing dataset by specifying the name of the dataset, or interactively specifying a projection and a datum and their associated parameters. In this case, youll be specifying a predefined coordinate system.
6. Click Select on the Spatial Reference Properties dialog box.
The wizard opens the Coordinate Systems folder.
ArcGIS provides many predefined coordinate systems for you to use, stored as .prj files. The files include all the coordinate system parameters including the map projection type and parameters, measurement units, and so on. You can also define custom coordinate systems and save them as .prj files (for example, the state_dot.prj file).
7. Double-click Geographic Coordinate Systems and double-click North America.
8. Click North American Datum 1983.prj and click Add.
The coordinate system information is displayed in the Details window.
9. Click OK to close the Spatial Reference Properties dialog box, then click Next.
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The wizard summarizes the coordinate system definition information.
10. Click Finish.
The coordinate system of the river shapefile is now defined. To verify this, in ArcCatalog navigate to the County_share folder, click river, click the Metadata tab, and click the Spatial tab. The coordinate system is now listed as GCS_NorthAmerican_1983 (you may need to close ArcCatalog and restart it to see this).
Project the shapefile
When you define a coordinate system, you simply tell ArcGIS what projection the dataset uses and what units the coordinates are stored in. When you project a dataset, on the other hand, ArcGIS actually creates a new dataset with the coordinates transformed from the existing coordinate
units (in this case, decimal degrees) to a new coordinate system (in this case, Transverse Mercator meters). You specify the input dataset and the coordinate system to project into, and ArcGIS creates the new dataset.
Because you have data that is already in the Transverse Mercator coordinate system used by the City, you can simply specify a dataset to match to. The wizard will get the coordinate system parameters from the existing dataset and create a new river shapefile in that coordinate system.
1. In ArcToolbox, double-click Project Wizard.
2. Click the Browse button on the wizard and navigate to the County_share folder under the project folder.
3. Click river.shp and click Add.
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The shapefile name and coordinate system you defined appear in the window.
4. Click Next.
The wizard asks you to specify a name for the projected shapefile and a location where it will be stored. Youll put it in the City_share folder since it will eventually become part of the Citys database. Youll name it river02prj since it will be the second version of the river dataset and will have been projected.
5. Click the Browse button and navigate to the project folder. Double-click City_share, then type river02prj in the Name text box.
6. Click Save.
The City_share folder is listed as the location to store the projected shapefile river02prj.
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7. Click Next.
The wizard asks you for the coordinate system into which to project the river shapefile.
8. Click Select Coordinate System.
The Spatial Reference Properties dialog box appears.
This is the same dialog box you used to define the coordinate system for the lowland shapefile and the river shapefile. In those cases you specified a spatial reference (.prj) file. This time youll specify an existing dataset from which to get the coordinate information. You know the parks feature class is in the right coordinate system since you copied it directly from the Citys existing geodatabase.
9. Click Import and navigate to the WaterProject geodatabase under the project folder connection.
10. Click parks_polygon and click Add.
The dialog box displays the coordinate system, and you can see its the correct one: PCS_Transverse_Mercator (PCS stands for Projected Coordinate System).
11. Click OK to close the dialog box.
The wizard presents a summary of the output coordinate system parameters.
12. Click Next.
The wizard shows you the output extent of the projected file.
13. Click Next, then click Finish.
The Project Wizard projects the river shapefile to match the coordinate system of the data in the Citys database. The projected shapefile, river02prj, is saved in the City_share folder.
14. Youre finished using ArcToolbox, so go ahead and close it by clicking the x in the upper-right corner of the window.
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