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1. In the ‘Layer Properties: MajorRoads’ window, click Cancel.
2. In the Contents pane, double-click the Schools layer to open the 'Layer Properties' window.
3. In the left menu, ensure the Source tab is still selected and expand the Spatial Reference section.

Note that the Schools feature class uses the same geographic coordinate system as the MajorRoads feature class: GCS North American 1983. Even the general projection type is the same: Lambert Conformal Conic. However, its properties have been modified to be suitable for all of Texas, rather than just the South Central portion of Texas, so the Projected coordinate system name is now Texas Centric Mapping System/Lambert Conformal. The Texas Centric Mapping System is an example of a statewide projection that is suitable for mapping the entire state. Statewide projections are commonly developed for large or elongated states, such as Alaska, California, Michigan, and Texas, which would otherwise be divided into numerous small bands using the State Plane system.

1. In the ‘Layer Properties: Schools’ window, click Cancel Cancel.
2. In the Contents pane, double-click the County layer name to open the 'Layer Properties' window.
3. In the left menu, ensure the Source tab is still selected and expand the Spatial Reference section.

Note that the spatial reference is in an Unknown Coordinate System, meaning that the coordinate system of this feature class has not been defined. In other words, ArcGIS does not know which coordinate system the data was created in and, therefore, will probably not be able to accurately line up this data layer with other data layers. Before you can reliably use this feature class, you will need to define its coordinate system and projection.

1. In the ‘Layer Properties: County’ window, click Cancel.

The geographic coordinate system and projection for each of the three feature classes are summarized in the table below.

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Displaying Undefined Layers

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1. At the top of the Contents pane, right-click Map  Map and select Properties.
2. In the menu on the left, select Coordinate Systems.

Notice that, indeed, the State Plane Texas South Central projection is listed.

1. In the ‘Map Properties: Map’ window, click Cancel.
2. In the Contents pane, right-click on the  the MajorRoads layer and select Zoom to Layer.

Notice that both the MajorRoads layer and the Schools layer appear to line up properly, even though they have different projections. This is because ArcGIS is able to perform “on-the-fly” projection, as long as the coordinate systems of both layers are defined. On-the-fly projection means that the Schools layer is being superficially displayed in the State Plane Texas South Central projection of the data frame, based on calculations performed by ArcGIS; however, the projection of the Schools feature class itself has not been altered from the Texas Centric Mapping System projection.

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1. In the Contents pane, right-click on the County layer and select Zoom to Layer.

Notice that the County layer does not appear on where it should on the Map. If you zoom out enough, you will see that it is in the middle of the Pacific Ocean This is because ArcGIS does not know where to locate the County layer relative to the other layers, since it is not defined. Instead, ArcGIS does the best it can and treats the coordinates of the County layer as if they were in Texas South Central State Plane coordinates, even though they are not.

1. In the Contents pane, right-click on the MajorRoads layer and select Zoom  Zoom to Layer.
2. Double-click Map to open the 'Map Properties' window.
3. Ensure the General tab is selected.

Notice that the 'Map units' are in feet. We will make the display units match the map units.

1. Use the 'Display units' drop-down menu to select US Feet and click OK.
   
   
   
   

Notice when you move your cursor around the map display, the coordinates listed in the bottom right of the window are similar to those shown below, indicating units of millions of feet.

1. In the Table of Contents, right-click the County layer and select Zoom to Layer.

It is evident that both layers are being drawn in the data frame, but ArcGIS simply does not know how to line them up properly. Notice when you move your cursor around the map display now, the coordinates are similar to those shown below, indicating units around -95 and 29 feet.

Whenever you come across X-coordinates between -180 and 180 and Y-coordinates between -90 and 90, you can be fairly sure that they are actually geographic coordinates of latitude and longitude listed in decimal degrees. The fact that Houston is located at 95° W, 29 N° is further confirmation that the county layer was created in a geographic coordinate system, rather than a projection. In this case, ArcGIS is treating these measurements of decimal degrees as if they were measurements of feet in the State Plane Texas South Central System, with the end result of locating Harris County in the middle of the Pacific Ocean.

1. Right-click the MajorRoads layer and select Zoom to Layer.

Whenever you encounter this type of situation, where two layers show up in the Contents pane, but do not line up as you expect them to, you know it is most likely a projection problem.

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Now that you know the geographic coordinate system of the County feature class, you will need to define it so that ArcGIS knows, as well. Please note that the geographic coordinate system and projection must be defined based on metadata provided from the data source itself. If you cannot locate such metadata, you should contact the provider of the data for such information. You cannot simply guess or decide which projection to use when defining the data (though, occasionally, you may have to resort to educated guesses and trial-and-error when metadata absolutely cannot be tracked down.)

1. On the ribbon, click the Analysis tab.
2. In the Geoprocessing group, click the Tools button to open the Geoprocessing pane on the right.
3. In the Find Tools search bar, type "define projection".
4. Click the Define Projection tool to open it.
5. Use the ‘Input Dataset or Feature Class’ drop-down menu to select County.
6. For the 'Coordinate System', click the Select coordinate system button to the right of the drop-down menu.
7. In the Coordinate System window, expand Geographic coordinate system > North America > USA and territories.
8. Click NAD 1983 and click OK.
9. Ensure your Geoprocessing pane appears as shown below .At and click Run at the bottom of the Geoprocessing pan, click Run at the bottompane.

Notice that the County layer has been projected onto the correct location of Harris County.

1. In the Catalog pane, double-click the County layer.
2. Select the Source tab and expand Spatial Reference.

Notice that the Geographic coordinate system is now listed, since you have defined the feature class.

1. In the ‘Layer Properties: County’ window, click Cancel.

Projecting Data

If you are only interested in creating a visual map, as you have done now, then relying upon on-the-fly projection will suffice. If, on the other hand, you are interested in performing any sort of calculations between the layers that rely upon distance, area, or spatial overlap, then it is recommended that you use the same projection for all layers. In addition, you can only measure linear distances in a projected coordinate system, not in a geographic coordinate system, so the County layer would need to be projected anyway, before any sort of measurements could be made.

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Projecting Layers

1. At the top of the Geoprocessing pane, click the Back arrow.
2. In the Find Tools search bar, type ‘project’ ‘project’.
3. Click the Project tool.
4. For 'Input Dataset or Feature Class', use the drop-down menu to select the County layer.

Note that the output dataset is saved to the same geodatabase as the input dataset and the name of the output feature class has the suffix “_Project” tacked onto the end of the original input feature class name.

1. For ‘Output Coordinate System’, use the drop-down menu to select the MajorRoads layer.

Notice that the NAD 1983 State Plane Texas South Central projection has been imported from the MajorRoads layer. While you could have again navigated to the projectionyourself, in this case, you know that the same coordinate system is already used by the MajorRoads layer. In such an instance, it is easier to import the coordinate system from another layer, especially if you are not familiar with where the coordinate system of interest is stored.

1. Ensure that your Geoprocessing pane appears as shown below and click Run Run.

When previously defining a layer, you simply updated the metadata attached to that layer to include the known coordinate system and projection. When projecting a layer, you have actually created a second copy of the data in the new coordinate system. The original layer stays in the native coordinate system and the new layer is converted to the desired coordinate system.

1. In the Catalog pane, right-click County_Project and select Properties. Navigate to the Source menu and expand Spatial Reference.

Note that the Geographic coordinate system is still GCS North American 1983 and that the new coordinate system is NAD 1983 StatePlane Texas South Central FIPS 4204 Feet.

1. In the ‘Feature Class Properties’ window, click Cancel. In the ‘Layer Properties: County_Project’ window, click Cancel.

You will now repeat the same process to re-project the Schools feature class from the Texas Statewide Mapping System projection into the State Plane Texas South Central projection.

1. Repeat steps 3-7 with the Schools layer. When your Geoprocessing pane looks like the one shown below, select Run.

All of your layers have now been projected into the State Plane Texas South Central projection.

1. In the Contents pane, right-click the Schools layer and select Remove.
2. In the Contents pane, right-click the County layer and select Remove.

Since all layers in your data frame are now in the same projection, you could proceed to make accurate calculations of distance and area between the layers.Last updated August 14, 2018.