Practical Navigation - All about maps
First published in OutdoorX4
I recently received the following response to a request I had made for sheets of a particular US Army map series:
Dear Mr. Jackson,
We have checked our collection of sheets comprising the Army Map Service (U.S.) set of East Africa maps (LC call number G8320 s250 .U51). Unfortunately we found no sheets corresponding to the sheet code numbers that you gave us. Also checking the index sheet for the entire collection, there were no marks indicating that we had ever received those sheets.
Sincerely yours,
Cartographic Reference Specialist
Geography & Map Division
Library of Congress
Washington, DC 20540
Let me point out the most important points in this communication unless you missed them: ‘no marks indicating that we ever received those sheets’ and ‘Library of Congress’. To request a map that the Library of Congress does not have must be a rare map indeed, especially one produced by the US Army. Not finding that map made me think of a question I have been asked several times in navigation classes at the Overland Expo; in the age of GPS and Google Earth are paper maps (or maps in general) still useful? On the face of it, a reasonable question (navigation die-hards, stay with me), but lets explore why maps are still critical to what we, as overlanders do, and what maps are best. In later articles I’ll cover using maps with GPS and the use of Google Earth for trip planning and recording.
The Keys to Navigation
There are two aspects to navigation. The first is position, and the second is route. That’s a glib way of saying ‘where am I now?’, and ‘how do I get to where I want to go?’ Many view position as just the coordinates of where you are, your current waypoint if you like, but a useful position is much more than that. It has to have some reference to features on the ground and be located relative to them. This is where a map comes in, and hopefully a good map, be it electronic or paper. A brief example will help illustrate this:
Let’s say you are on the emergency contact list for a friend who is on a great overland trip through the Americas down to Ushuaia. You get a call for help with the position of N17.29159° latitude and E-89.54068° longitude, but that’s all. Where is your friend? Based on the waypoint alone we can’t tell much. She is north of the Equator by 17 degrees (latitude is positive so north) and west for the Central Meridian by 89 degrees (longitude is negative so west), but is that the Southern US, Mexico or Central America? Without some other reference we can’t even tell which country she is in, or even if she is on land or at sea. Would a satellite image help? See Figure 1 from Google Earth. I purposely switched off all the overlays on this image so that it is just the satellite image and not a map (more on this later). Now if you plot the waypoint, we can add the following information: she is on land and it looks like she is in a highly vegetated area north of some farmland. There are some lakes to her southeast and either a lake or the ocean to her southwest, but beyond that, we can’t say much. Now let’s plot her position on a real map; see the map image, Figure 2. Now we are getting somewhere; from the map we can glean a lot of information. To start with your friend is in northern Guatemala in jungle cover. The lake to the southeast is Laguna Yaxhá, and the water body to the southwest is Lago Petén Itzá not the ocean. Two towns are close by, Tikal and Uaxactún, and there is a track running south from Uaxactún through Tikal and down to the lake. We can also see that there are airstrips at both Tikal and Uaxactún, information that may be critical in a rescue. Zooming in (Figure 3) we can even see that she is located at an archeological site called El Encanto, is approximately 200 meters above sea level and is approximately five miles due east of the Uaxactún Tikal track. The picture includes much of the margin information on the map for a reason. The scale, the key, the location diagram and other very important information is recorded on map margins and is part of what makes a ‘good map’. Getting help to your friend just went from a vague dream to a real possibility.
So now that we have the position part of navigation out of the way, I hope it will be pretty obvious that a map will be critical for deciding how to get from point A (where we are) to point B (where we want to go). The term ‘it’s all relative’ applies in navigation like no-where else, and maps are key to this, so let’s examine the critical aspects of maps.
What is a map?
At it’s most basic, a map is a picture of a landscape as a flat surface viewed from directly above. Useful maps have the added requirement of showing features such as relief, lakes and vegetation and man-made features like roads, towns and cities (and airfields as seen on the Joint operations Graphic used in the above example). They will also show ‘virtual’ information like borders and geographic coordinates as either latitude and longitude or UTM/UPS (Universal Transverse Mercator / Universal Polar Stereographic). Finally, they will have a scale so that distances can be measured. The scale is just a ratio of units on the map to units on the ground. A scale of 1:250,000 means one inch on the map is equal to 250,000 inches on the ground and also means one centimeter on the map equals 250,000 centimeters on the ground (the scale is unitless). The larger the scale the more area the map covers and the less detailed it will be. Large scale maps (1:1,000,000 or higher) are great for overview planning, while smaller scale (1:100,000 or below) are great for detailed navigation. The scales between 1:100,000 and 1:1,000,000 are what I generally shoot for for operational maps; they provide enough of an overview for general routing, but enough detail for navigation to campsites and the like.
Pure satellite imagery as shown in the Google Earth image for the example above passes the requirement for a basic map, but not a useful one. Google Earth calibrates their imagery to add the geographic coordinates and uses overlays to add all the other critical information, although relief is still a bit sketchy; see Figure 4. With the overlays enabled Google Earth produces excellent maps, but they always require a network connection (or a massive amount of cashe memory), so backcountry use is limited. What other options are there?
Types of Maps
There are three types of maps we need to be concerned with, and some special cases. The most obvious are the old-fashioned paper maps, which, so long as they meet the critical criteria outlined above are still excellent for both planning and navigation. Second are scanned map images that can be used on computers. These are referred to as raster maps or raster image maps, for the simple reason that they are a pure image of the map and, while they can be calibrated with geographic coordinates for location finding, cannot be used for routing on GPS units or computers. These maps can either be used as an image like a paper map (on either computer, tablet or smartphone), or can be imported into a mapping program like Ozi Explorer (for Windows) or MacGPS Pro (for Apple) where they can be calibrated to allow seamless coordinate information. The Joint Operations Graphic map used in the example above was calibrated in MacGPS Pro allowing the supplied waypoint to be located. Graphic formats for these map images vary and can be almost anything, but calibrated versions are usually geo PDFs or PICTs. The third and last are the true vector maps that can be used for routing. These are the maps that can be installed on GPS units and are the maps supplied for smartphone and tablet routing apps. The vector in vector map refers to the way the digital information is supplied, in this case as a distance and a direction allowing the device to determine a route between two points.
The special case maps are the online maps. Google Earth was already mentioned. It provides raster images that are calibrated. Google Maps, Apple Maps, Waze, and all the other smart app maps are vector based, but the information is stored on the internet and downloaded as needed, meaning that a network connection is required. With a few exceptions (Gaia GPS, Hema 4WD Maps App and Tracks4Africa to name three) this makes for cumbersome, or even impossible backcountry use.
Choosing Maps
For paper maps in the US, the obvious source is the USGS topographic series on which most of the following maps are also based. The main issue with the USGS maps are the fragile paper and age of the information; some sheets have not been updated since 1961. (See: store.usgs.gov). Both US Forest Service and the Bureau of Land Management have some excellent maps, though limited to their areas. The US Forest Service Motor Vehicle Use Maps are great for planning purposes, as they show what trails are open to motor vehicle use.
Private map producers like DeLorme and National Geographic provide some excellent topographic maps. In the case of the former, the DeLorme Atlas & Gazetteer series have pretty much been the gold standard for overland reference for years, with a volume for each state and useful information like public land boundaries. One of my favorites has always been the Trails Illustrated series, which was purchased by National Geographic at some point, but still has the Trail Illustrated name. These are plastic maps with excellent trail and trail use information, though the Arcadia map is disappointingly limited on information.
For electronic maps, all of the USGS topographic series can be bought in geo-referenced versions. Mac GPS Pro sells these as do others. Avenza (avenza.com) produces geo-referenced PDF maps for use with their smart-device app, and are now offering the National Geographic Trails Illustrated line as digital maps. I won’t cover the obvious electronic maps like Google Maps and Apple Maps mentioned before.
For international maps, the optional are more diverse. National Geographic makes the Adventure Map series that includes places like Guatemala, Belize, Botswana, Baja North, Baja South and the Yucatán. Avenza also sells geo-referenced PDFs of some of this series; see Figure 5 which shows a screenshot off my iPad of the National Geographic Belize Adventure Map with the waypoint for our wayward friend marked. Other options for paper include the International Travel Maps (ITM) series, some of which come in tear-proof plastic versions. I can’t speak with much authority on their maps for the rest of the world, but their Central American maps are abysmal. The Honduras and Nicaragua maps are littered with mistakes; roads where none exist, town names that are completely wrong (Las Minas on the map is really Los Mangos, Rio Blanco is really Rio Bianco etc.). Their Morocco map seems better, but it would take a lot for me to trust it. The Michelin maps tend to be good, and Hema Maps are excellent, though their form factor when folded is a bit large for my taste and the separate hard cover adds little and makes the map unwieldy.
Online resources for maps are many and varied, but some of the best I have found follow. For raster images, the University of Texas at Austin (lib.utexas.edu/maps/) has a brilliant and ever-expanding collection both for the US and the rest of the world. For routable vector maps, my expertise lies in the Garmin platform, so sites like GPSFileDepot.com and garmin.openstreetmap.nl are excellent. In the latter case you can select areas of the world that you want and generate a Garmin compatible map usable on both Garmin BaseCamp and Garmin GPS units. The only issue with this is that all of the maps generated have the same name (OSM Routable), so it can really mess with the database of installed maps for BaseCamp. I use a free program called JaVaWa GMTK to rename the maps to something useable, which allows many to be installed. Gaia GPS I already mentioned briefly, but they allow maps to be downloaded and used on smart devices without an internet connection. So does Tracks4Africa, though that is limited to the African continent.
And last of all, there is the Library of Congress (loc.gov) that has an incredible map collection, many of which they are scanning and putting online for free. Unfortunately if you are looking for maps in certain obscure areas of East Africa, even the Library of Congress falls short, though they can’t be blamed; further research uncovered that those maps were never made in the first place.