How to Download 7.5 Minute Series USGS Topo Maps
December, 2010
Mick Womersley
MASAR Resource Officer
Unity College SAR
What follows are instructions for downloading free .tif files of the 1:24,000, 7.5 minute series (meaning 7.5 minutes of longitude and latitude per map) USGS topographic maps for use in Maine Search and Rescue, from the Maine Geographic Information Systems Library run by state government (know as MEGIS).
A .tif file is a common-format, computer photo file. If you browse the Internet and look at family photos on your computer you already have software to access and read these files.
These maps are US government property and so legally in the public domain and free for all to use. However, the printed versions now cost six or eight dollars apiece, so the online maps are a great help.
Please circulate as freely as you wish.
To download the files:
1. Find the map you want by title. These are the same titles printed on the map. Usually the nearest Town is the title, often with a directional qualifier, so for instance my house is on the "Brooks East" quadrangle, despite being in Jackson (because Brooks is the largest settlement on the map and so the map is named for Brooks). You can get the titles for all Maine USGS 7.5 minute topo quads using the USGS Map Store map locator using this link.
http://store.usgs.gov/b2c_usgs/usgs/maplocator/%28ctype=areaDetails&xcm=r3standardpitrex_prd&carea=%24ROOT&layout=6_1_61_48&uiarea=2%29/.do
2. Using a web browser such as Firefox or Internet Explorer, go to the MEGIS Catalog portal (click on this embedded link):
http://megis.maine.gov/catalog/catalog.asp
3. Go to the tab menu for "Tile" files. "Tiles" are picture files designed for use in GIS programs, but if a file is a picture file, you don't need a GIS program to open it.
4. Search for the title you want under 'drgclips". The "drgclips" section, which is the first section under MEGIS Tiles, is the ine that has all the 1:24,000 maps. Follow the MEGIS menus to download the map files to your computer. Save these files to a labeled file folder.
5. Open the map files in an image/photo viewer such as Preview or Adobe reader. In most cases your computer will do this automatically if you click on the image icon or thumbnail in your file folder.
6. You can zoom in, zoom out and print the map at any size of enlargement you want, or just read it on your computer. You can also "tile" multiple maps together to make composite maps in documents using either a GIS program (there is now a free GIS program called Q-GIS - a little complicated, but you can puzzle it out) , or more simply using Microsoft Power Point.
(If you tile together a Microsoft Power Point image of your unit's area and email it to me, I can print a 42-inch poster-size image on our college's plotter for you and mail it back to you - a handy resource to have in the SAR Cache.)
To use the files in SAR operations and training:
1. The 7.5 map data is the same as the data in the DeLorme Atlas and in the GIS programs used by the Warden's Service. The GIS programs add satellite imagery, which is what is normally handed to search team leaders at the start of the search. But these 7.5 minute topos have additional useful information. They are, however, often several years out of date as to buildings and roads. In almost all cases, however, the topography (ie contours, waterways, and landforms in general), is accurate, and this is most useful. Also the UTM grid is present on most of these maps which makes finding and using GPS coordinates very easy. Finally, the UTM grid can be used as a map grid to take compass bearings from the map to use on the ground much more easily than can be done with the satellite hand-outs. This is most useful when a Silva-type compass is used because these compasses are designed to be see-through so you can identify direction of travel and the map grid looking through the compass plastic, and line them up properly.
2. First step: print your map at the proper scale. This may take trial and error, enlarging and reducing images in your printer viewer until you get it right. You can print about a quarter of a map at a time at the 1:24,000 scale using regular US letter copy paper. The UTM one-kilometer grid on the map should be about 1 and 5/8 of an inch across when you get the scale right.
Remember, this is a one-kilometer grid, so even if you don't get the scale right, you still have a scale if you understand the grid squares to be one kilometer across (on the ground) and estimate from there.
3. To use these maps on a search and rescue operation, I suggest you them use it side-by-side with the satellite imagery given out by the Wardens Service. Take the maps into the field and make comparisons as you navigate to, from, and around your search areas. The contour and waterway information is the most useful as this will help you find routes over rough terrain.
4. Take care using GPS. In many cases these 1:24,000 series maps are fitted to an out-of-date GPS datum, NAD 27, and have the UTM grid also fitted to this datum printed on the map as an overlay. MEGIS deleted this information when they made the "tiles." There are ways to infer it using a GPS or other maps, but all too complicated to describe here. The Warden's Service Satellite imagery uses WGS 84 and lat-long coordinates, which can be many meters different than NAD 27. So although the UTM grid on the map can be used for taking compass bearings, it can't be used for radioing coordinates back to the CP unless you make sure the CP is looking at the same map. This is just likely to cause confusion and I would avoid it unless there is some very good reason, such as the possibility that you're using a trail or road that is marked on the map but not on the satellite.
(Having said this, knowing how to give and use a proper 8-figure UTM coordinate as well as a lat-long coordinate is a good SAR skill. UTM coordinates are very much easier to use in the field with a map, and very handy for training purposes. The US military has used them for many years. We now teach this skill to all Unity CLE graduates along with the traditional Lat-Long system.)
Hope this is useful to you.
Happy mapping.
Mick Womersley
MASAR Resource Officer
Unity College SAR
MASAR Resource Officer
Unity College SAR
What follows are instructions for downloading free .tif files of the 1:24,000, 7.5 minute series (meaning 7.5 minutes of longitude and latitude per map) USGS topographic maps for use in Maine Search and Rescue, from the Maine Geographic Information Systems Library run by state government (know as MEGIS).
A .tif file is a common-format, computer photo file. If you browse the Internet and look at family photos on your computer you already have software to access and read these files.
These maps are US government property and so legally in the public domain and free for all to use. However, the printed versions now cost six or eight dollars apiece, so the online maps are a great help.
Please circulate as freely as you wish.
To download the files:
1. Find the map you want by title. These are the same titles printed on the map. Usually the nearest Town is the title, often with a directional qualifier, so for instance my house is on the "Brooks East" quadrangle, despite being in Jackson (because Brooks is the largest settlement on the map and so the map is named for Brooks). You can get the titles for all Maine USGS 7.5 minute topo quads using the USGS Map Store map locator using this link.
http://store.usgs.gov/b2c_usgs/usgs/maplocator/%28ctype=areaDetails&xcm=r3standardpitrex_prd&carea=%24ROOT&layout=6_1_61_48&uiarea=2%29/.do
2. Using a web browser such as Firefox or Internet Explorer, go to the MEGIS Catalog portal (click on this embedded link):
http://megis.maine.gov/catalog/catalog.asp
3. Go to the tab menu for "Tile" files. "Tiles" are picture files designed for use in GIS programs, but if a file is a picture file, you don't need a GIS program to open it.
4. Search for the title you want under 'drgclips". The "drgclips" section, which is the first section under MEGIS Tiles, is the ine that has all the 1:24,000 maps. Follow the MEGIS menus to download the map files to your computer. Save these files to a labeled file folder.
5. Open the map files in an image/photo viewer such as Preview or Adobe reader. In most cases your computer will do this automatically if you click on the image icon or thumbnail in your file folder.
6. You can zoom in, zoom out and print the map at any size of enlargement you want, or just read it on your computer. You can also "tile" multiple maps together to make composite maps in documents using either a GIS program (there is now a free GIS program called Q-GIS - a little complicated, but you can puzzle it out) , or more simply using Microsoft Power Point.
(If you tile together a Microsoft Power Point image of your unit's area and email it to me, I can print a 42-inch poster-size image on our college's plotter for you and mail it back to you - a handy resource to have in the SAR Cache.)
To use the files in SAR operations and training:
1. The 7.5 map data is the same as the data in the DeLorme Atlas and in the GIS programs used by the Warden's Service. The GIS programs add satellite imagery, which is what is normally handed to search team leaders at the start of the search. But these 7.5 minute topos have additional useful information. They are, however, often several years out of date as to buildings and roads. In almost all cases, however, the topography (ie contours, waterways, and landforms in general), is accurate, and this is most useful. Also the UTM grid is present on most of these maps which makes finding and using GPS coordinates very easy. Finally, the UTM grid can be used as a map grid to take compass bearings from the map to use on the ground much more easily than can be done with the satellite hand-outs. This is most useful when a Silva-type compass is used because these compasses are designed to be see-through so you can identify direction of travel and the map grid looking through the compass plastic, and line them up properly.
2. First step: print your map at the proper scale. This may take trial and error, enlarging and reducing images in your printer viewer until you get it right. You can print about a quarter of a map at a time at the 1:24,000 scale using regular US letter copy paper. The UTM one-kilometer grid on the map should be about 1 and 5/8 of an inch across when you get the scale right.
Remember, this is a one-kilometer grid, so even if you don't get the scale right, you still have a scale if you understand the grid squares to be one kilometer across (on the ground) and estimate from there.
3. To use these maps on a search and rescue operation, I suggest you them use it side-by-side with the satellite imagery given out by the Wardens Service. Take the maps into the field and make comparisons as you navigate to, from, and around your search areas. The contour and waterway information is the most useful as this will help you find routes over rough terrain.
4. Take care using GPS. In many cases these 1:24,000 series maps are fitted to an out-of-date GPS datum, NAD 27, and have the UTM grid also fitted to this datum printed on the map as an overlay. MEGIS deleted this information when they made the "tiles." There are ways to infer it using a GPS or other maps, but all too complicated to describe here. The Warden's Service Satellite imagery uses WGS 84 and lat-long coordinates, which can be many meters different than NAD 27. So although the UTM grid on the map can be used for taking compass bearings, it can't be used for radioing coordinates back to the CP unless you make sure the CP is looking at the same map. This is just likely to cause confusion and I would avoid it unless there is some very good reason, such as the possibility that you're using a trail or road that is marked on the map but not on the satellite.
(Having said this, knowing how to give and use a proper 8-figure UTM coordinate as well as a lat-long coordinate is a good SAR skill. UTM coordinates are very much easier to use in the field with a map, and very handy for training purposes. The US military has used them for many years. We now teach this skill to all Unity CLE graduates along with the traditional Lat-Long system.)
Hope this is useful to you.
Happy mapping.
Mick Womersley
MASAR Resource Officer
Unity College SAR
No comments:
Post a Comment