Advanced Geographic Information Systems

Using the ArcView Projection Utility

The ArcView Projection Utility is a stand-alone wizard-based tool which lets you project shapefiles from one coordinate system to another. It lets you project unprojected shapefiles, and perform datum transformations, including NADCON--the standard method of converting between NAD27 and NAD83 within the continental United States.

The utility also provides a way for you to create coordinate system metadata for your shapefiles which do not already have that information. That information is stored in an ASCII projection file, which has the same prefix as your shapefile, and a .prj extension. For example, if you have a shapefile called rivers.shp, its coordinate system information is kept in rivers.prj file.

When you project or reproject your shapefiles, those shapefiles are not touched--the utility makes new shapefiles in the coordinate system you specify. You can use the ArcView Projection Utility without the interface, from the command line of a DOS prompt. More conveniently, you can also use the utility as an extension to ArcView.

To use this extension, check the Projection Utility option on the Extensions list. With your view active, select ArcView Projection Utility from the File menu. It will take a few moments for the utility to initialize, but once it does you will see the first of several dialog boxes.

Clicking on the Help button of the Step 1 dialog will open a detailed help file for the utility. When the help file opens, clicking the Help Topics button will open a help menu that is fuller still. Double-click on "Projection Utility" to see this menu. You might want to consider working through the Quick Start Tutorial to acquaint yourself with the projection conversion process. Later, as you progress through the various steps, you can press Help to learn more about each wizard panel.

Once the extension is loaded, the Projector icon should appear as part of your View menu in ArcView - its icon looks like a small north arrow in a box toward the right side of the View menu.

Here are some quick steps you can use to project one shapefile:

• Step 1 in the wizard. Press Browse, then navigate to the data directory that contains the shapefile you need to reproject. Double-click on the shapefile. The Browse window closes and your shapefile appears in the wizard. Press Next on the Step 1 wizard.

• Step 2 in the wizard. If the shapefile you selected has projection information stored with it, the wizard will read this information and display it in this dialog. If your shapefile does not have any projection information stored with it, you must tell the utility which projection parameters are used for this shapefile. The parameters for all the ArcView sample data are:
  • Coordinate System Type: Geographic
  • Name: GCS_North_American_1927 [4267]
  • Units: Degree [9102]
• Check Show Advanced Options, if it is not already checked. Note that the Parameters, Datum, and Ellipsoid tabs are now displayed.
• Click on the Datum tab.
  • Changing coordinate systems usually includes transforming between datums. On this tab, you can control this transformation.
  • If only one Geographic Transformation method is available, this field will be grayed out and that method will be used. If more than one method is available, you can set it here. For most cases, you should use the default method.
  • Were you to transform some sample ArcView data to NAD83, you would choose NAD_1927_To_NAD_1983_NADCON from the Geographic Transformation list.
• Press Next.
• You are prompted to save the projection parameters with the shapefile. Answering Yes permanently stores the parameters you just entered in a projection file (.prj) which is stored with the input shapefile. If you store the parameters, the ArcView Projection Utility will read the information from this file the next time you project this shapefile, and you won't need to fill in the fields yourself. Since you don't have write access to shapefiles on the C: drive, answer No. If you are projecting shapefiles from your H: drive, you may select Yes.

• Step 3 in the wizard. Here, you enter the parameters for the output shapefile.
  • If you want to unproject your shapefiles to decimal degrees, choose Geographic, then choose the appropriate values from the Name and Units fields.
  • If you want to project or reproject your shapefiles, choose Projected, then choose the appropriate values from the Name and Units fields.
  • Created with the new shapefiles are projection files (.prj). These files store the information about the coordinate system the shapefiles were created with.
• Press Next.

• Step 4 in the wizard. By default, the new shapefile is written to the current working directory with the name Newshape.shp. If you want to change the location or the file name, press the Browse button. The Save As dialog appears. Enter a new file name, and/or navigate to the folder you want to store the new shapefile in (a directory where you have write access). If you want to store the new shapefile in a new folder, press the New Folder button. A new folder appears in the dialog - simply type a new name for it, then double-click on it to open it.
• Press Next.

• The Summary panel lists the input and output information for your shapefile. If all is in order, press Finish.
• A progress bar appears. A message appears when processing is complete. Click OK. Your shapefile is now projected!
• Add the new shapefile as a theme to a view in ArcView to verify the output.