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1. In the Catalog pane, expand the Databases section and the HydrologyLab.gdb geodatabase.
2. Drag the Watersheds feature class into the Lab2 map view.
3. In the Contents pane, double-click the Watersheds layer.
4. In the ‘Layer Properties’ window, click the Source tab.
5. Scroll down and expand the Spatial Reference section.

Notice that the layer is in a geographic coordinate system called NAD 1983, which stands for North American Datum 1983. Because the data has a geographic coordinate system, the coordinates are stored in degrees, which indicate the three-dimensional location of the data on Earth's spheroid. Though the data itself is stored in a geographic coordinate system, your computer monitor is flat, so, even though no projection has been defined, the data must be displayed in a particular projection. Whenever ArcGIS displays data in a geographic coordinate system, it uses a pseudo plate carrée projection, where one degree of latitude by one degree of longitude is represented as a square, rather than a curved trapezoid. In other words, all lines of latitude and longitude are evenly spaced. This type of projection results in stretching in the east-west direction, which increases the farther north or south from the equator you are mapping.

1. Close the ‘LayerProperties’ window.

Working with geographic coordinate systems is fine for creating purely visual maps, as you did in Lab 1 (though the visual distortion can be disorienting and misleading), but, in this lab, you will be calculating areas, distances, and overlaps between features. Such calculations require the three-dimensional coordinates to be projected down onto a two-dimensional plane, so that the coordinates are stored in linear units, such as feet or meters, rather than degrees. In order to facilitate measurements of distance and area, you will now project the Watersheds layer into the State Plane Texas South Central projection which is best suited to mapping the greater Houston region.

1. In the Analysis tab, click the Tools button to open the Geoprocessing pane.
2. In the 'Find Tools' search box, type "Project".
3. Click the Project (Data Management Tools)tool.
4. For ‘Input Dataset or Feature Class’, use the drop-down menu to select the Watersheds layer.
   
5. For ‘Output Dataset or Feature Class’, rename “Watersheds “Watersheds_Project” Project” to “Watersheds_StatePlane”, since that is the name of the projection you will be using.
6. Next to the ‘Output Coordinate System’ box, click the Set Select Coordinate System button.
7. Double-click Projected Coordinate Systems → State Plane → NAD 1983 (2011) (US Feet).
8. Select NAD 1983 StatePlane Texas S Central FIPS 4204 (US Feet) and click OK.

Because both the input and output coordinate systems are based on the NAD 1983 geographic coordinate system, no geographic transformation is required.

1. Ensure your ‘Project’ window appears as shown below and click Run.
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   Image Added Geoprocessing Pane.
   
   

Now that you have the correctly projected layer, you no longer need the original NAD 1983 layer.

1. RightIn the Contents pane, right-click the original Watersheds layer and select Remove.
2. Double-click the new Watersheds_StatePlane layer.
3. Scroll down and expand the Spatial Reference section.
   

Notice that the layer is now in a projected coordinate system, NAD

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1983

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StatePlane

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Texas

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S Central FIPS  4204 (US Feet).

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1. Close the ‘Layer Properties’ window.

You may have noticed that the visual appearance of the watersheds did not change in your Map Display, even though you projected them. That is because the data frame takes on the projection of the first layer added to it. Since you first added the original unprojected Watersheds layer into the data frame, which was in NAD 1983, the data frame still displays the data in NAD 1983 (or

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psuedo plate carrée). Currently, the projected Watersheds_StatePlane layer is being projected-on-the-fly back into NAD 1983 for visual purposes

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.

Move the cursor around the screen and notice that the coordinates

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at the bottom

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of the

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map view are shown in decimal degrees. This is another clue that the data frame is still using a geographic coordinate system; however, you would like the data frame to display data using the local Houston projection.

1. At the top of the Contents pane,  rightdouble-click the Lab 2 map title and click Propertiesto open the 'Map Properties' window.

2. Click the Coordinate System Systems tab.

While you could search for or navigate to the State Plane Texas South Central

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projection, as you did before, in this case, you know that the same coordinate system is already used by the Watersheds_StatePlane layer. In such an instance, it is often easier to import the coordinate system from another known layer, especially if you are not familiar with the hierarchy of the coordinate system folders

1. Scroll to the top of the 'XY Coordinate Systems Available' list.

2. Expand Layers.

Notice that all of the coordinate systems used by layers currently in the map are displayed. You can expand the coordinate systems to determine exactly which layers are stored in which coordinate systems.

1. On the ‘Coordinate System’ tab toolbar, click the Add Coordinate System button and select Import….
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2. Double-click the HyrdologyLab geodatabase.
3. Select the Watersheds_StatePlane feature class and click Add.
   Notice that the familiar State Plane Texas South Central projection is now listed

   Click NAD 1983 StatePlane Texas S Central FIPS  4204 (US Feet)

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4. Click OK.
   
   Notice that the watershed boundaries are now more compact in the east-west direction, as expected, because the local projection results in less distortion than the Plate Carrée projection used to represent geographic coordinate systems.
   
   

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1. In a web browser, go tohttps://viewer.nationalmap.gov/basic/.
   
   First you will select the data products you are interested in viewing and downloading.
   
   
2. On the left side bar, check the ElevationProducts(3DEP) section to expand it.
3. Within the Product Search Filter, check1/3 arc-second DEM for the subcategory and selectArcGrid for the File Format.
4. On the left side bar, scroll below the Elevation Products section and check the Hydrography (NHDPlus HR, NHD, WBD) section to expand it.
5. Within the Product Search Filter, selectNational Hydrography Dataset (NHD) for the subcategory, selectHU-8 Subbasin for the Data Extent and selectFileGDB10.1 for the File Format.
   
   Now you constrain your downloads to your area of interest.
   
   
6. In the search bar just above the map on the right, type “Houston” and clickGo.
   
   After zooming into Houston, you can see the blue boundaries of the individual subbasins and each subbasin is labeled with its HUC-8 number on the map.
   
7. Near the center of the map, click within Subbasin 12040104 to select it.
   
   Notice that just above the map, your search is now constrained to Polygon: huc8 12040104.
   
   
8. At the top of the left side bar, clickFindProducts.
   
9. Under Available Products, to the right of Elevation Products (3DEP), clickresults.
   
   You are now provided with a listing of all the DEM tiles covering the area of Subbasin 12040104.
   
10. In turn, click Download for USGS NED n30w096, n30w095, and n31w096.
    
11. Navigate to the location where the three zipped folders have been downloaded.
12. Select and copy all three zipped folders.
13. Using Windows Explorer, navigate to your HydrologyLab folder.
14. Paste all three zipped folders directly inside your HydrologyLab folder. Do NOT paste them inside the .gdb geodatabase.
15. Select all three zipped folders.
16. Right-click any of the three selected folders and select 7-Zip → Extract to “*\”, which will create one unzipped folder for the contents of each zipped folder.
17. Return to ArcGIS Pro.

Since you just added new files to your folder, you will need to refresh it in order for them to appear in the Catalog pane.

1. Click the Project tab on the Catalog pane.
2. Right-click your HydrologyLab folder and select Refresh.
3. Expand n30w095 and the other folders to preview their contents.

Each raster file with a name such as grdn30w095_13 corresponds to a 1x1 degree tile. The file name contains “grd” for grid, followed by the latitude and longitude of the top left corner of the tile.

Ading Adding raster data in ArcMap

1. Drag the grdn30w095_13 raster into the Map Display.

You will be asked if you would like to create pyramids. Pyramids cache the raster at multiple reduced resolutions, resulting in an increased file size, but better rendering performance in your Map Display. It is normally a good idea to create pyramids, but since you will be processing the corresponding rasters into a new file in the next step, you will not create pyramids at this time.

1. Repeat Steps 1 and 2 with the grdn30w096_13 and grdn31w096_13 rasters.

Notice that the 1x1 degree tiles appear as angled rectangles, because they are being displayed in the State Plane Texas South Central projection. If the data frame were still in the NAD 1983 geographic coordinate system, the tiles would look like squares. Now you will look up the native coordinate system of the raster files.

1. In the Contents pane, double-click the grdn31w096_13 layer.

Under the Source tab, scroll down and notice the spatial reference is listed as GCS_North_American_1983. Since this coordinate system is not the same one currently used by the data frame, the raster layer is being projected-on-the-fly into the State Plane Texas South Central projection.

Mosaicking raster files

The edges where the three tiles meet are currently visible, because the minimum and maximum elevation is different in each raster, causing the same value to be represented with a different shade of gray in each raster. To solve that visual problem and also simplify future processing steps, you will mosaic the three rasters into a single raster.

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1. In ArcToolbox, back in the Raster toolset, double-click the Raster Processing toolset and click the Clip (Data Management) tool.
2. For ‘Input Raster’, drag in the DEMStatePlane layer from the Contents pane.
3. For ‘Output Extent’, drag in the Watersheds_StatePlane layer.
4. Check Use Input Features for Clipping Geometry.

Checking that box ensures that the raster is limited to the actual shape of the watersheds, rather than a rectangle covering the same extent.

1. For ‘Output Raster Dataset’, rename the raster from “DEMStatePlane“DEMStatePlane_Clip” to “DEMSubbasin”Clip” to “DEMSubbasin”.
2. Ensure your ‘Clip’ window appears exactly as shown below and click Run.
   
   

1. Remove In the Contents pane, remove the DEMStatePlane layer from the Contents pane.
2. Turn off the Watersheds_StatePlane layer to view the DEMSubbasin layer.

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1. In Geoprocessing pane, click the Spatial Analyst Tools toolbox, click the Map Algebra toolset, click the Raster Calculator tool.
2. In the list of ‘Rasters’, double-click the DEMSubbasin layer.
3. In the calculator, double-click the * button.
4. In the equation box, type “3 “3.281”281”, which is the conversion factor from meters to feet.
5. For ‘Output raster’, rename the raster from “rastercalc” to “DEMft”“DEMft”.
6. Ensure your ‘Raster Calculator’ window appears as shown below and click Run.
   
   

Visually, the meters and feet layers should be identical, but if you look at the layers in the Contents pane, you will notice that the original layer goes from elevations of -8 to 62 meters and the newly calculated layer goes from elevations of -26 to 204 feet.

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1. Again, go back to the Raster Calculator tool. Delete the previous expression.
2. In the list of 'Rasters’, double-click the DEMft layer.
3. In the calculator, double-click the <= button.
4. In the equation box, type “15” “15”.
5. For ‘Output raster’, rename the raster from “demft_raster” to “Flood15ft”“Flood15ft”.
6. Ensure your ‘Raster Calculator’ window appears as shown below and click Run.
   

1. Close Geoprocessing pane.
2. Right-click the Flood15ft layer. Click Symbology.
3. In the table of values, right-click the 0 value and click Remove.
   
   
   

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1. 
   
2. Click the rectangle symbol to the left of the 1 value and select Blue.
   
   Image Modified

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1. Save your

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1. project.

Now the cells containing an elevation of 15 feet or less are highlighted on top of the elevation raster.

FOR MAP LAYOUT TO BE TURNED IN

Create an 8.5 x 11 layout showing the DEM clipped to the subbasin with areas less than or equal to 15 feet in elevation highlighted.

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