Map Projection Using ArcGIS - CEProfs

1 Map Projection Using ArcGIS Prepared by Francisco Olivera, , and Srikanth Koka Department of Civil Engineering Texas A&M University October 2003 Contents Brief Overview of Map Projection Using ArcGIS Goals of the Exercise Computer and Data Requirements Procedure 1. Projections of the world 2. Projections of the United States 3. Projections of Texas 4. Defining projections 5. Projecting data Using ArcToolBox Brief Overview of Map Projection Using ArcGIS Map Projection involves taking spatial data defined on the curved surface of the earth and transforming it to the flat surface of a map.

2 A map Projection is the mathematical algorithm used for this transformation. ArcToolBox permits the transformation of data from one map Projection to another. Goals of the Exercise This exercise will introduce you to ArcGIS for projecting GIS data. Computer and Data Requirements This exercise has been successfully completed Using ArcGIS All data needed for this exercise is contained in the geodatabase. Download the file containing the geodatabase, which is in the same folder where this document is located. Unzip it and save the files to a working directory in your computer.

3 2 Procedure 1. Projections of the world a. View of the world in geographic coordinates (longitude and latitude) Open ArcMap from the Start menu and click on the New Map File button to create a new empty map document. To add data to your map, click the AddData button and browse to the geodatabase in your working directory. Double click on the geodatabase to access the feature classes inside it. While pressing the Ctrl key, select the Cntry94 and World30 feature classes, and then click Add. If necessary, drag World30 below Cntry94 so that the layout of the countries is superimposed on the 30-degree squares.

4 To show just the World30 layer outlines, in the table of contents, right click on World30 and then on Properties/Symobology. Under the Symbol frame click on the rectangle filled with color. On the left hand side of the Symbol Selector form, you can see a list of color schemes, select the one named Hollow, click OK and then click OK in the Layer Properties wizard. You can now see the world in geographic coordinates. To label the countries, right click on the Cntry94 layer, select the Label Features option in the drop down menu. To customize the label display, right click on the layer, and then click on Properties/Labels.

5 To remove the labels, unselect the Label Features in this layer option. To label a few selected countries, if the Draw toolbar doesn t appear in the ArcMap document, use View/Toolbars/Draw to add it to the map. On the Draw toolbar, click the down arrow beside the NewText button, and select the Label option. In the Labeling 3 Options choose the Placement and Label Style of your preference, and close the form. Click on the countries you want to label. Finally, save the project as Move the cursor around on the view and you will see a pair of numbers to the bottom right of the ArcMap window.

6 These numbers are the coordinates of the cursor and from the values displayed you can see that they are in decimal degrees of latitude and longitude. b. View of the world in Robinson Projection The map Projection of cntry94 and World30 is geographic; however, they can be viewed in different Projection systems. A common Projection system for the world is the Robinson Projection . Create a new data frame in ArcMap Using Insert/Data Frame. Add the World30 and Cntry94 feature classes to this new data frame by right clicking on Add Data. Again rearrange the layers and change the legend of World30 as explained in the previous case.

7 To view the world in Robinson Projection , right click on the data frame and click on Properties/Coordinate System. In the Select Coordinate System box, click on Predefined/Projected Coordinate System/ world /Robinson ( world ), and click OK. A warning message appears, click yes. You will see the world in Robinson Projection . Refresh the map by clicking on the Full Extent tool, and then save the document. The Robinson Projection is a world map Projection designed to present the whole earth with a minimum of distortion at any location. If you move the cursor over this space, you'll see that the coordinates are now in a very different set of units, meters in the projected coordinate system.

8 4 c. View of the world "from space" (not available in ArcGIS ) Create a new data frame and add to it the World30 and Cntry94 feature classes. Again, rearrange the layers and change the legend if necessary. To view the world "from space", change the data frame coordinate system to Predefined/Projected Coordinate System/ world /The world from the Space. As before, a warning message appears, click Yes. Refresh the map by clicking on the Full Extent tool, and then save the document. Try looking at the world from above College Station. You can get the coordinates of locations on the earth by viewing earth in the geographic Projection .

9 Play around a bit. 5 2. Projections of the United States a. View of the United States in the geographic coordinates Click on the New Map File button to create a new map file, and save it as Add the States and LatLong feature classes to the data frame. These data are polygons of the states of the United States and lines forming a 5-degree grid of latitude and longitude. Click on the Zoom In tool and zoom into the conterminous United States. If necessary, use the Pan tool to move the map to the center of the window. b. View of the United State in Albers Equal Area Projection The Albers Equal Area Projection has the property that the area bounded by any pair of parallels and meridians is exactly reproduced.

10 That is, the Projection preserves the correct area, although it somewhat distorts the direction, distance and shape. Create a new data frame and add States and LatLong. To view the United States in Albers Equal Area Projection , right click on the data frame and click on Properties/Coordinate System. In the Select a coordinate system box, click on Predefined/Projected Coordinate System/Continental/North America/ USA_Contiguous_Albers_Equal_Area_Conic and click OK. Compare the shape of the United States in geographic coordinates and in Albers Projection . You can see that, in geographic coordinates, the United States appears to be wider and flatter than it does in Albers Equal-Area Projection .