You can use these procedures to import elevation data from the USGS National Map website.
The first step is to obtain the data for importing.
- Open the National Map Viewer in your web browser.
- Zoom into your area of interest. It may be quicker to type in the city, state to get started. It is helpful to click on the [Imagery] button to help find the area. As you refine your area, you may even want to consider changing the aspect of the browser window to fit.
- Click the Download Data link at the top and choose “Click here to download by current map extent”. This is one part of the process that makes the resulting data managable.
- A dialog appears with “USGS Available Data”. If you are interested in the plan view map(s), see the section below. For now turn on he Elevation toggle near the bottom and choose GridFloat. Click he [Next] button.
- You will be presented with several options. For the best quality with only data *inside* the viewer window, look for the item that is labeled as “Dynamic” with a type of “Elevat 1/3” and place a check in this record. Then click the [Next] button.
- At this point you will see a red dashed rectangle around the area o be returned, confirming what you should receive.
- Click the [Checkout] button, enter your email address and click the [Place Order] button. There is no charge for this service.
- In a few minutes you will receive an email with a link you can click to begin downloading the data in a ZIP file.
- Extract the ZIP file to a folder in preparation for the import.
The next step is inside CAD (with MapWorks 4.0 loaded).
- Open the existing drawing or create a new empty drawing to receive the imported data.
- Establish the drawing’s coordinate system. This uses the PrjDwgSys command (found in the menu under Map Projections). The downloaded data is in Lat/Lon and will need to be projected.
- Import the points in the downloaded data.
A) Initiate the SurPltAll command (found under Surfaces).
B) Click the [Load] button and navigate to the extraction folder.
C) Find and select the FLT file in the folder (likely the largest file in the folder), click [Open].
D) The dialog will display information about the file, notice the coordinates are in lat/lon and the elevations are in meters.
E) Verify the source/target systems and click [Zoom Extents].
F) Change the “Draw As” option to 3D Points for the smallest data, unless you simply wish to plot the 3D Faces for visualization.
G) If your drawing coordinate system is feet, change the vertical exaggeration to 3.2808 and change the base field to 0.0.
H) Click the [OK] button to begin plotting the points.
You are now ready to contour the points or create a grid to use for profiles, cross sections, etc. If you used 3dFaces, you are ready for visualization, try the new SurColRng (Surface Analysis Color) to color the resulting faces based on their elevation (or slope).