The Projection Extension for ArcView 3.0 or 3.1
You have two datasets for the same area that you have downloaded and imported into ArcView, but then you discover you can only view them one at a time. What's the use of that? The whole point of GIS software, like ArcView, is to be able to view different sources of spatial data in relation to each other.
Most of the time, this problem is a result of datasets being in different projections.
There are three or four common projections used for Wyoming datasets, and literally hundreds used through the U.S. and the world. What projection your dataset is in depends on where you got it, what area it covers, and its source (the original map or database it was derived from).
ArcView can be confusing because supposedly it can do "projections on the fly" - change your dataset from one projection to any other projection simply by selecting an option off the menu. This however is only true if the data is originally in geographic coordinates, or more specifically in decimal degrees (latitude/longitude expressed as decimals instead of degrees, minutes and seconds).
As long as your datasets are stored in decimal degrees, you can view them simultaneously in the same View and "project" that view to whatever projection you desire, by selecting the View Properties option off the View menu. This is not a permanent projection. Your data is still in decimal degrees. ArcView is only temporarily changing the View to match the selected projection.
In order to do a permanent projection change, or to change one dataset to match the same projection that another one is so that you can view them simultaneously, you either need ARC/INFO (which costs many thousands of dollars) or you need the free Projector extension for ArcView.
The Projector extension is a sample extension, which comes with ArcView version 3.0 or 3.1, but must be installed before it can be used. You will need to copy the extension file, prjctr.avx, from ArcView's software samples directory into the program extension directory.
|Windows/NT users:||Unix users:|
Copy the prjctr.avx files from:
Copy the prjctr.avx files from:
(These directory names might vary somewhat depending on your system and the version of
ArcView you have installed.)
Now when you open ArcView, you should be able to activate the Projector extension from the Project Manager, by selecting Extensions off the File menu.
Once the Projector extension is activated, it will create a new button on your button bar.
When you click the projector button, you may get this error message:
View units must be set before projecting. Stopping.
If you get this message, select the View properties option off the View menu.
Then, set the map units. Usually you will select either decimal degrees, meters, or feet, depending on what projection your data is currently in. Not sure what projection the data is in? Hopefully, your data came with a metadata document. This is a text file that contains all the information about the dataset, including its projection information, which can be found under the Spatial Reference Information section.
Once your map units are set, click the Projector button again. Now it will ask you to enter the existing projection information. Again, refer to the metadata document to make sure you enter the correct information. In this example, the data is in Universal Transverse Mercator, North American Datum of 1927, or UTM 27 (a world coordinate system). After selecting UTM 27, you will also need to select the zone (in this case, zone 12) that your data is in.
After setting the input projection, then you are prompted to enter the output units and the projection that you want to change the data to. In this example, we want to change it to Lambert, another common statewide projection for Wyoming. Lambert Conformal Conic. This is not a world coordinate system, so you need to select "Projections of the United States" from the Category list, and then select "Lambert Conformal Conic" from the Type list.
You can also customize the parameters that are used for the Lambert Conformal Conic projection. Before pressing OK, click on the Custom button, which then allows you to alter the origin and standard parallel parameters. The parameters shown here are the ones that we find work well for Wyoming.
After clicking Ok, ArcView then asks you if you want to recalculate area, perimeter and length fields - almost always you want to select YES for this.
Finally, ArcView will ask you what name and location you want to use for the newly projected file that it will create for you.
One last important note about the Projection extension: it cannot accurately convert datums, only projections. If you have data in the North American Datum 1927 and some other data in the NAD 1983 datum, you can't solve this problem in ArcView - you need ARC/INFO or some other software to do this conversion. Also, the Projectior extension can only project feature themes (point, line or polygon). It cannot project grid or image themes.