USGS Topographic Maps: Converting GeoPDF to GeoTIFF
After more than 60 years, the USGS topographic maps still provide an excellent way to explore the United States. The content and symbology are consistent and easily recognizable, and they serve both as a reliable data source and a basemap. Since 2009 the USGS has begun offering the US topographic maps through a new map series called US Topo. The US Topo Map program shares topographic maps based on GIS data in GeoPDF format. These GeoPDFs serve as a nice, standalone products, but lacks certain functionality desired by the GIS community. By converting these GeoPDFs into a more useable format, such as GeoTIFF, it is possible to create a seamless mosaic of an area, providing an unbroken view of multiple topographic maps and a great basemap option.
This post assumes that you have access to Global Mapper v15 and Esri ArcGIS for Desktop 10.2.2, and a basic knowledge of how to use them.
First, download the US topographic maps for your area of interest. You can find instructions on doing this in the “Using the National Map Viewer to Download US Topo Maps” blog posting.
- The next step is to transform the GeoPDFs to GeoTIFFs. To do this, we will use Global Mapper 15 and the following script, which was modified from an existing USGS workflow document; the shapefile template needed to remove collars from the US Topo maps can be downloaded at the following link.
Here is some more important information about this script:
- This script will create two outputs from the input GeoPDFs – 1) collared GeoTIFFs and 2) collarless GeoTIFFs.
- Collarless GeoTIFFs are created using a clipping template to remove the collar from the topo map (please see the underlined “POLYGON_CROP_FILE” potion of the above script).
- This script will create and store the output GeoTIFFs (both collared and collarless) in the same folder as the original GeoPDF files.
- This script will maintain the original coordinate system of the GeoPDFs. All GeoPDFs are stored in the UTM Coordinate System – in this case, the Assateague Island topographic maps are stored in UTM Zone 18N.
- The “with collar” exports will be 8-bit TIFFs with a color map. Colors may differ from original GeoPDF colors, however the file size will remain nearly the same.
- The “collarless” exports will be 4-band RGBA TIFFs. Colors will be retained, however file size will be large.
- To run the script:
- Make sure the file extension is set to .gms so that Global Mapper will recognize the script.
- To successfully run this script, place it within the same folder as the original GeoPDF files. It will also be necessary to place the All_7.5min_cells.shp (part of the file download at the above link) and accompanying files into the folder containing the original GeoPDFs.
- Within Global Mapper, click the File tab at the top of the page, and scroll down to Run Script.
- Browse to the correct folder and select your script with the .gms extension. Click OPEN.
- This will open the Script Processing Window. In the top half of the window you can view your script. In the bottom half of the window you will see the results of your script. This is where you will see a running ‘commentary’ of the script as it successfully (or unsuccessfully) processes.
- Finally, click RUN SCRIPT at the bottom of the Script Processing Window.
- Depending on the amount of GeoPDFs and your computers processing speed, this process could take an hour or more.
- When the script has completed running, bring one collarless and one collared GeoTIFF into ArcMap to determine if the script correctly processed the images.
If you have no border area around your collarless GeoTIFFs, then you are finished. If you HAVE a border area, please proceed to the next step. Please be aware this could be a very small collar! Zoom in to the edges of your images to determine this.
If the collarless GeoTIFF appears to have a slight border (yellow, black or white) around it, that’s okay. This is due to the fact that as of now, ArcGIS does not recognize TIFF6 Transparency (this should be changing when 10.3 is released).
To double check if there is a white border around the collarless topographic map, change the color of your data frame to a non-white color. To do this, follow the steps below:
Double click on the Layers heading the Table of Contents (red circle) and navigate to the Frame tab (purple circle). In the Background dropdown menu, choose a non-white color (green circle).
Now we will clip off the remainder of the “residual collar.” This method will require the user to manually clip off the residual collar from each GeoTIFF file. For an alternative method to removing the residual collars, please visit page 27.
- Bring all collarless TIFFs for your AOI into ArcMap. Turn off all but one layer in the Table of Contents (this makes processing easier).
- Zoom in to this layer.
- Use the Draw toolbar (accessed from the Customize > Toolbars menu) to create a polygon that only covers the extent of the topo map, excluding the border area.
- With the newly created graphic still selected, click on the dropdown menu on the Draw toolbar and select the Convert Graphic to Feature option.
- Within the pop-up window, select the output location and name of the layer you will create.
- Also check the box to automatically delete the graphic after the conversion takes place.
- When prompted, click YES to add the new feature to the map.
Next, open the attribute table of the newly created dataset, select the single feature contained within, and then close out of the window.
Now, open the Clip tool from the Data Management toolbox.
- Select the correct input raster.
- For the output extent, select the new feature we just created.
- Check box = Use input features for clipping geometry
- Select the output location and file name. Make sure to include the file extension in the name!
- For example your output name should look like this: Topo_Example.tif
- Click OK to run tool.
- Add the new raster to ArcMap to ensure that the collar has been completely clipped away.
It will be necessary to repeat this process for each TIFF that has a residual border.
Note: It will be necessary to move the clipping template feature class to the location of each TIFF. It may also be necessary to edit the vertices of the polygon to properly line up along the edges of the topo map.
To move the location of the clipping template, and to edit the vertices when necessary, begin an editing session (to open the Editor toolbar, go to Customize > Toolbars).
Once the process of removing the residual collars has been completed, please remove the stretch that is automatically applied to each collarless TIF image. This can be done in one of two ways:
Option 1: Open the Properties of each image, select the Symbology tab and change Stretch Type to None.
Option 2: Create a batch process with the “Set Raster Properties” tool (Data Management toolbox) and select “Processed” from the Data Source Type dropdown menu.
You should now have a seamless collection of topographic maps that can be added into a mosaic dataset for easy, seamless viewing and simple sharing.
For more information on creating a mosaic dataset, please refer to the Creating a Mosaic Dataset from Orthophotos blog post for instructions.
This blog posting was developed with the support of a competitive grant (cooperative agreement number P09AC00212; task agreement number P13AC00875) from the National Park Service in partnership with the North Atlantic Coast Cooperative Ecosystems Studies Unit. It is part of a larger document available for download on the IRMA Portal.