Creating Custom Topographic Maps for your Hand Held GPS Unit - Part 2

This is Part 2 of a multi-part series on creating custom topographic maps for your hand held mapping GPS unit. For previous posts click one of the following:
Creating Custom Topographic Maps for your Hand Held GPS Unit - Part 1

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Creating Custom Topographic Maps

for your Hand Held GPS Unit - Part 2

Finding and Downloading Data

In Part 1 we discussed the steps required to produce a topographic map for a mapping GPS unit and the tools we will use. In this post I will walk you though the process of downloading data from the internet.

For this tutorial I am going to create topographic maps with hydrography data. These maps will overlay the existing maps in your GPS unit, this way, if you have Garmin Street Navigator maps, you will still be able to see the Garmin Data beneath your custom map. I will eventually post an advanced How-To that includes the shape files for park boundaries, but this requires quite a bit more work and is not necessary for creating a basic topographic map.

Step two in our process is downloading data. We will start with the topographic data from the USGS after the jump.


Open your web browser (I am a dedicated Firefox user, but for this operation I use Internet Explorer.  Firefox sometimes has issues running scripts and the following sites are very script intensive) and navigate to:

http://seamless.usgs.gov/website/seamless/viewer.htm

The above link takes you to the USGS Seamless Viewer. Using this interface we will select the topographic data we require for our map. The biggest difficulty in using the USGS viewer is responsiveness. It is not a snappy interface so please be patient.

The USGS Viewer

On the left hand side of the viewer are the navigation tools, on the right are the data filters. To make navigation easier I would suggest going to the Elevation heading on the right and turning off the NED Shaded relief and the GTOPO60 color shaded relief. This will make the interface quicker. Also to help find your area of interest I suggest going to the Places heading then the Boundaries heading, again on the right and turning on the GNIS Cities (with labels) and the Counties and County Labels. Again, this is all to aid you in locating your area of interest.

Once you have located the area that you want data for, select the Define Rectangular Download Area tool on the left hand side under Downloads. Left click and drag your mouse to define a box. This should select all the data in and around your area of interest. After you complete the selection, a pop-up window will appear.

The Pop-up Window

In this window we will select Modify Data Request. This will allow us to change the default data and select our data formats.

Modify Data Request window.

Under the Elevation heading choose either the National Elevation Dataset (NED) 1/3 Arc Second or the National Elevation Dataset (NED) 1/9 Arc Second option and uncheck the National Elevation Dataset (NED) 1 Arc Second option. The 1/3 Arc Second data is very detailed and the 1/9 is even more so. For my needs the 1/3 Arc Second is plenty accurate enough.

Also make sure you change the data format from ArcGRID to GeoTIFF. Next scroll to the bottom of the window and under the Delivery Options change the "Maximum size (MB) per piece" from 100MB to 50MB. This will make the data files more manageable. Click the Save Changes & Return to Summary button.

You should now have a window that looks similar to this:

Click the Download buttons on each Data Set to save the files to your computer. Make sure to save the files to an easy to find location on your computer. I suggest creating a TMP folder in your C Drive and saving them here. The closer to the C Drive that you locate your data, the simpler our GDAL commands will be when it comes to creating our topographic lines.

Next we are going to download Hydrographic data from the USGS 'National Hydrography Dataset' viewer found at:

http://nhdgeo.usgs.gov/viewer.htm

This viewer is similar to the USGS Seamless viewer so it should have a familiar feel. Again, navigation tools are on the left and data filters are on the right.

NHD Viewer. Very similar to Seamless

Zoom into your area of interest. Now, here's the tricky part. The USGS Topo data that you selected will be very nice rectangular areas. The NHD data is broken up based upon subbasins. A subbasin is basically a drainage area for a tributary. They have no regular shape so you must download data for every subbasin that your topo data crosses. Unfortunately sometimes this is not very obvious since your topo data selection was an arbitrary rectangle that you drew on the map. It sometimes takes several trips to the NHD to grab all the necessary data. Don't worry about having too much hydro data for you map. We can trim your hydro data in MapEdit to match your topo data area.

On the right hand side, click on the NHD High Res heading. If there are no options under this heading, you have not zoomed in far enough. Once you are the options for this data set will appear. When they do, place a check next to the NHDFlowline, NHDArea, and NHDWaterBody options. Under the Hydrologic Units heading, place a dot in the circle next to the Subbasins option.

Your selections should look similar to the above picture.

Next, select the Polygon Extract tool on the left side of the screen. With this tool. click just once inside the subbasin that you want. This will bring up a window:

In this box we need to select High Resolution under Option #1 and Shapefile Under Option #2. Leave Option #3 blank and provide your email address under #4. Within an hour up to a day you will receive an email with a download link to your data. Again, like the topo data, save the file in an easily locatable directory.

Well that's all for this phase of the map building process. In the next part I will discuss preparing the contour data and creating topographic line shapefiles with the FWTools Shell. Stay tuned!

~Occasional Hyker