Downloading and Preparing GIS Precipitation Data Layers Using ESRI ArcMap Presented by William Merkel Hydraulic Engineer, NRCS 11/7/2018 NRCC Precipitation

Create a Directory to Save data Working with GIS data, it is always best to organize the data into a directory. 11/7/2018 NRCC Precipitation

Open Internet and go to www.precip.net 11/7/2018 NRCC Precipitation

Open Data & Products 11/7/2018 NRCC Precipitation

Select GIS Data Files 11/7/2018 NRCC Precipitation

Select Data Type, Duration, Recurrence For this example, select Data Type: “Return period Estimates”, Duration: 30 min, and Recurrence: 10 yr. 11/7/2018 NRCC Precipitation

Select Save 11/7/2018 NRCC Precipitation

Select a directory and file name If more than one grid dataset will be saved in this directory, it is recommended to enter a unique file name at this point. output.asc is a default name. 11/7/2018 NRCC Precipitation

After Download Complete, Close 11/7/2018 NRCC Precipitation

Open Documentation and GIS Shapefiles Download the state/county map of New York and New England from Documentation / Outreach Documents / GIS Shapefiles. 11/7/2018 NRCC Precipitation

Select Save 11/7/2018 NRCC Precipitation

Save it in directory It is recommended to save this file in the same directory as the precipitation layer saved previously. The state/county map need only be downloaded once. It is used as an overlay to the GIS grid for location purposes and used later to assign a GIS projection to the precipitation layer. 11/7/2018 NRCC Precipitation

After Download Complete, Close 11/7/2018 NRCC Precipitation

Right Click, Extract to here 11/7/2018 NRCC Precipitation

Layer named NE_states_counties_WGS72 is unzipped The map of states and counties in New York and New England is now available to open in a GIS. The map is in the WGS 1972 projection. 11/7/2018 NRCC Precipitation

Open ESRI ArcMap 11/7/2018 NRCC Precipitation

Open a new empty map, click OK 11/7/2018 NRCC Precipitation

Click the Add Data icon 11/7/2018 NRCC Precipitation

Add map of northeast states 11/7/2018 NRCC Precipitation

The map should look similar to this. 11/7/2018 NRCC Precipitation

Change map to No Color Right click on the purple color in legend to open the color selection window. Changing the map to No Color will show only the state and county boundaries. It will allow the precipitation data to be visible after it is added later. 11/7/2018 NRCC Precipitation

Map will show state and county boundaries 11/7/2018 NRCC Precipitation

Open ArcToolbox Window 11/7/2018 NRCC Precipitation

Select Conversion Tools, To Raster, and ASCII to Raster Double click the ASCII to Raster command. 11/7/2018 NRCC Precipitation

Select Input file, Output name, and FLOAT Use the browse icon to the right of each file name box to select directory and file names. Use the pull-down icon to the right of the Output data type data box to select FLOAT. 11/7/2018 NRCC Precipitation

After conversion is complete, Close 11/7/2018 NRCC Precipitation

The precipitation grid is added to the map The precipitation grid at this point is temporary. The values in the grid need to be divided by 1000 to convert the values to inches. 11/7/2018 NRCC Precipitation

Select Spatial Analyst Tools, Math, and Divide 11/7/2018 NRCC Precipitation

Select Input raster, divide by 1000, and Output Raster name Use the pull-down selection to the right of the Input raster name to select the layer named ASCIITo_outp1. Edit the Output raster name to represent that the grid is 30 minute duration and 10 year recurrence interval. 11/7/2018 NRCC Precipitation

When the Divide operation is complete, Close 11/7/2018 NRCC Precipitation

The grid 30min_10yr is now prepared 11/7/2018 NRCC Precipitation

Change color scheme of the grid, optional Left click on the color ramp of the layer to open the Select Color Ramp window. 11/7/2018 NRCC Precipitation

Colors have been changed. 11/7/2018 NRCC Precipitation

Right click, open layer properties Open layer properties to see what projection is assigned to the grid. 11/7/2018 NRCC Precipitation

Spatial Reference (projection) is undefined To do any more work with this grid, a projection needs to be assigned. In fact, the projection of this grid must be defined to be the same as the map of state/county boundaries that is shown in this ArcMap project. Close properties by clicking OK. 11/7/2018 NRCC Precipitation

Select Data Management Tools, Projections and Transformations, and Define Projection Double click to open the Define Projection command window. 11/7/2018 NRCC Precipitation

Select Input Dataset using pull-down selection Select Input Dataset using pull-down selection. Click Find Icon to the right of Coordinate System. Click the icon to the right of the Coordinate System data box to select a projection. 11/7/2018 NRCC Precipitation

Select Import Select the Import button so the projection of the state/county map can be used. 11/7/2018 NRCC Precipitation

Select NE_states_counties_WGS72.shp Click Add button. 11/7/2018 NRCC Precipitation

Click Apply The projection of the state/county map will be assigned to the 30 minute 10 year grid layer. 11/7/2018 NRCC Precipitation

Click OK 11/7/2018 NRCC Precipitation

Click OK to start command operation 11/7/2018 NRCC Precipitation

Close when command is completed. 11/7/2018 NRCC Precipitation

Open layer properties to check assigned projection Right click on 30min_10yr grid name and select Properties. 11/7/2018 NRCC Precipitation

Correct projection is assigned. The projection is set up in latitude and longitude coordinates. Close properties by clicking OK. 11/7/2018 NRCC Precipitation

Remove the temporary grid from the map window. Before the temporary layer (ASCIITo_outo1) can be deleted, it must first be removed from the map. Right click on the layer name and select Remove. 11/7/2018 NRCC Precipitation

Open ArcCatalog and browse to find asciito_outp1 . Delete it. Select the asciito_outp1 layer, right click and select Delete. 11/7/2018 NRCC Precipitation

asciito_outp1 is deleted from computer. Close Arc Catalog. 11/7/2018 NRCC Precipitation

Layer preparation is completed. At this point, the precipitation layer is complete. Now that a projection is assigned, the projection may be changed to another projection by using ARCGIS commands. 11/7/2018 NRCC Precipitation

Save the Project: Optional 11/7/2018 NRCC Precipitation

Save the Project: Optional Select a directory and enter a file name. Close ArcMap after project is saved. 11/7/2018 NRCC Precipitation

The End Questions ? This same process is followed to prepare GIS ASCII grid maps downloaded from the NOAA 14 web site. 11/7/2018 NRCC Precipitation