Frequently Asked Questions
Note: The answers on this page are targeted at map users for whom an accuracy of a few meters is sufficient. In some cases an answer or method presented is not the exact answer, but rather one that presents a somewhat simplified view that is more likely to be understood and used by the target audience. I'll try to mention when I've done this so that you can seek a more detailed understanding if you need it.
- Do you have a dealer in...?
- Do you sell maps?
- Do you have a tool for this scale?
- How durable are your tools? Will the ink wear off?
- The lat/lon ruler does not fit the lat/lon grid on my map. Why not?
- Can I set the declination on a Brunton 54LU compass?
- The UTM grid I have doesn't fit the grid on my map. What's wrong?
- Will you accept government credit cards or purchase orders?
- Is the information in the UTM booklet the same as the information on the web page?
- I'm getting the wrong answers on the UTM sample problem
- I'm getting the wrong answers on the lat/lon sample problem
- I put the coordinates for your sample problems into my topo map program, and they are out in the middle of the ocean! What am I doing wrong?
- Can you provide a free tool like...?
- When I print one of your pdf map tools, it is the wrong size or will not print. What can I do?
- Can you recommend a good GPS?
- I'm very bad at directions and maps, will a GPS help me?
- How do I set my GPS receiver to use UTM?
- Do I use UTM/UPS or User UTM Grid?
- What is the User UTM Grid setting used for?
- Which lat/lon format should I use?
- My GPS reading are consistently in the wrong position. What am I doing wrong?
- What kind of accuracy can I expect from my GPS?
- How can I tell if my map has UTM coordinates on it?
- What scale is my map?
- My map has a lat/lon coordinate markings but not UTM, can I use UTM?
- Can I use UTM with a road or street map?
- What kind of accuracy can I expect from my GPS?
- Drawing a UTM grid on a map that covers more than one utm zone
- Questions about using software map systems?
- What map software do you recommend?
- Is their any map software that runs on a Mac?
- What is the latitude longitude of...?
- How can I convert between UTM and Lat/Lon coordinates?
- How can I convert between different datums?
- Is UTM is another name for MGRS?
- Is the UTM system based on True North or Magnetic North?
- How do I calculate the distance between two points?
- What are the distances represented by a minute of latitude and longitude?
- Is the WGS84 datum more accurate than NAD27?
- What is UPS?
- How can I use my GPS to find the corners and boundaries of my property?
- I have two known points marked on the ground. Can I use my GPS to find the line between them?
- I want to use my GPS to make a map of some trails/roads. How do I do this?
- How do my SAR ground teams using UTM coordinate with aircraft using lat/lon?
- What format should our SAR team use for UTM coordinates?
- Should our SAR team use magnetic north or true north?
Here is a link to our dealer list. Most of these stores stock only a few of out most popular products. So it's a good idea to call ahead to check if they have what you are looking for.
Not directly. We have partnered with the folks at MyTopo to provide maps. Here are some hints and tips for ordering a map from MyTopo.
The cartographer or map maker selects a map scale based on the size of the area they are mapping and the size of the sheet the resulting map gets printed on. It's common to find map scales ranging from 1:1 all the way to 1:10,000,000.
The tools we sell, get printed in large batches, and we only do that for the popular map scales.
I am slowly expanding the number of scales that I stock. If you have a common scale for maps in your area, that you think I should stock, let me know, and I'll add it to the list under consideration.
In the past several decades, mapping projects done for an entire country are usually done by a government agency. Typically these agencies will select one or more scales to use for their map series. Using a consistent set of scales allows the maps sheets to be used adjacent to one another.
Cartographers making a single map of a specific area, like a park, often choose a scale to fit the area onto a reasonable or standard sized sheet of paper. The National Geographic Trails Illustrated map series is a good example. They use more than 60 different map scales in their series of several hundred maps.
As maps and map production move into the digital world it becomes very easy to adjust the output scale to satisfy your particular needs. Whenever it is reasonable to do so, you should stick with the more popular scales for printed maps. This will allow users of the map to use the map along with other printed maps of the area, as well as allowing them to use the common coordinate and distance measuring tools.
The UTM tools are printed on 30 mil clear stock, and then a protective coating is applied. We use either a film overlay or a UV cured clear coat. Repeated abrasion of the protective coating will eventually wear it off and then the markings will soon wear off as well. For day to day field use they seem to be quite durable. I tested this out by carrying one of the Pocket Corners around in my pocket with my keys and coins for a month. The tool developed a frosted look from the many small scratches it picked up, but the markings were all still there, and the tool was still quite usable.
If it is way too long east-to-west...
Remember the lines of longitude converge at the poles. That is to say the further north or south you go from the equator, the closer together they get. You need to use the ruler on a diagonal to compensate for this. Instructions are here.
If it is way too long north to south...
Not all maps use the same size lat/lon grid. You may be using a 7.5 minute ruler with a five minute grid spacing. In this case, only use the portion of the ruler from 0 to 5 minutes.
If it is way too short north to south...
Not all maps use the same size lat/lon grid. You may be using a 7.5 minute ruler with a 15 minute grid spacing. In this case, you will want to draw in additional grid lines to end up with a 7.5 minute grid spacing..
If it is just a bit too long north to south...
It turns out that the lines of latitude also get just a bit closer together as you move north or south from the equator. This is because the earth is an ellipsoid, not a sphere. MapTools lat/lon rulers are sized for an exact fit at 40 degrees north and south of the equator. For most of our users this will make the ruler about a millimeter too long. Most folks never even notice, and the results they get are well with in their accuracy requirements. To compensate for this you can use the ruler on a slight diagonal, much like you do when measuring longitude.
If it is just a bit too short north to south...
You may be further north or south than 40 degrees. But most likely the scale on your map is not quite correct.
I've seen an issue with my oldest DeLorme Atlas and Gazetteer for California. Puzzled, I did some more research and found that the old CA atlas was not really exactly a 1:150,000 scale. I ran out and bought a newer atlas, and it was right on. I ran all of the calculations for the length of my ruler, and double checked them against a USGS map as well. The ruler was correct.
My guess is that when the DeLorme Atlas series was first published, nobody was using the lat/lon lines since GPS receivers were not common back then. And a small error in a distance measurement would likely go unnoticed. On the other hand maybe the paper has stretched a bit, with years of use and less than ideal storage conditions. I've not been able to confirm the problem with DeLorme.
Only one or two customers have noticed this problem since I started selling the rulers back in 1999.
No, It will only give readings relative to magnetic north. See this FAQ answer for a reason why this may be the right thing to do anyway.
Usually this means the grid you are trying to align the tool with is not a UTM grid. The most frequent confusion come from the public land survey section lines. On a USGS 1:24,000 scale map they are dashed red lines, with red section numbers in the center, they roughly define a 1 mile grid. See this FAQ answer for some hints on locating the UTM grid marks.
Yes. We do a great deal of business with federal, state and local government agencies and are happy to accommodate your particular agencies purchasing requirements.
For the most part the information is the same. In a many places the booklet goes into more detail. The major difference is in packaging. The booklet provides a nice compact portable high resolution version of the information.
Don't align your grid tool with the edges of the map, called neat lines, they are NOT UTM grid lines in most cases. Line your grid up with the UTM Grid lines. When you are near the edge of the map, a portion of the grid may be off the map and you may need to use the value of a grid line that is not visible as the base of your coordinate measurement.
I put the coordinates for your sample problems into my topo map program, and they are out in the middle of the ocean! What am I doing wrong?
The maps and coordinates in the tutorials are fictional and are not intended to represent real locations. This should have no impact on their usefulness as an educational tool. A grid tool or ruler placed on the map will produce the expected answers. On the other hand, putting the coordinates into a computer based mapping system is not likely to yield useful information.
Most of my friends think I'm crazy for posting free copies on the of the things I'm trying to sell.
The short answer is that I'm not currently planning to expand the number of free downloadable tools that I make available. But, if you have a compelling reason for a particular tool to be downloadable, I'm willing to listen.
It's a balancing act. One hand I want lots of people to be able to learn to use map coordinates, so I provide lots of instructions and free versions of the tools for the most common map scales. No doubt I loose a few sales to folks whose needs are met by the free tools. But, I believe I gain more sales as people discover map coordinates, and find they want the quality and variety of tools available from the online store.
MapTools has evolved into a business with a significant investment in time, equipment, and inventory. It could have gone the other way, and been just a passion related to my search and rescue activities. In the end, I think I can provide the best quality tool to the most people using the business approach rather than the hobby approach.
Most of the "wrong size" problems have been related to page size and Adobe Acrobat's options that scale things to fit. Make sure the options "Shrink Oversize Pages to Paper Size" and "Enlarge Small Pages to Paper Size" are not enabled.
This is a bit like asking me what kind of car you should buy. Which GPS is right for you will depend on - what you want to do with it, how skilled you are at understanding new gadgets, and what your personal preferences may be.
That said, I do have some thoughts about what folks should consider when buying a GPS.
First a small disclaimer...
I don't sell GPS units or represent any GPS manufacturer. These opinions are my own. The uses I have for a GPS may be different than yours, so my recommendations may not apply. The product development cycle is short, new models are released frequently. As I do not spend much time looking at or lusting over each and every new model, my information may be out of date.
The most common uses I have for a GPS are:
- Getting a coordinate for my present location so that I can relate it to a map, save it for future reference, or report it to someone else by radio.
- Navigating to a known coordinate that I have entered into the GPS. Note that the GPS will only give you the straight line path as a distance and direction. On land, this is seldom the right path to follow.
- Recording a series of coordinates to use in adding a road or trail to an existing map.
- Hooked to a laptop in the car to create a moving map. I like to take out of the way dirt roads when I'm traveling. A bit of adventure for me and a good place to let the dogs out for a break. Using the moving map feature of programs like DeLorme's TOPO USA or National Geographic's TOPO! (Yes TOPO works on my Mac iBook!) you can plan ahead on where to turn off and have some idea where the dirt road will take you. Being able to power both the GPS and the laptop from the car is a good thing when you're operating like this.
Lucky for me almost all of the GPS receivers can preform these functions. I tend to be a minimalist when it comes to both price and extra features.
Here are some of the things I'm not willing to pay much extra for:
- - Built in maps
- Who wants to look at their topo map through a 1.5" X 3" window! Paper maps give you good detail and they let you see the relationship of the various terrain features that are around you. On the GPS you have to zoom out to see the surrounding terrain, and when you zoom out you loose the detail.
- Try it out, cut out a small window in a piece of paper and place it over your topo map, does it still seem as useful?
- Plus the paper map is a necessary backup that doesn't require batteries.
- - Color displays
- Since I'm not interested in loading it with map data, I don't have much need for a color display.
- - Built in compasses, altimeters, radios, mp3 players, etc.
- I prefer to have these as separate devices. My compass is low tech, light weight and has never run low on batteries. Same is true with my altimeter. My GPS is usually turned off and tucked away in my pack. I only use it continuously, when I'm recording a track, or getting very close to the destination coordinates that I'm seeking.
Here are a few features that I think are useful.
- Light weight, good battery life, uses 2 AA batteries
- WAAS (Wide Area Augmentation System)
- External Antenna
- "Map" display that shows current track and waypoints
- Dual position format display i.e. Lat/Lon and UTM
- Data port so you can transfer waypoints and tracks and use the moving map feature on your laptop topo program.
When I teach GPS classes, I usually group the students by GPS brand, so that they can help each other with the setup and operation details. The Garmin and Magellan groups are usually quickly on their way to the field problems while the Lowrance group is usually scratching their heads and looking at the manual. It seems the human interface Lowrance uses is just not as well thought out as the others. My observations do not necessarily reflect their latest models, they might have made significant improvements, as there has certainly been plenty of room to improve!
Some of the GPS units I own and why...
I own a dozen of these that I use teaching GPS classes. They're just $89 from Amazon, and have all the basic features. If you were going to own just one gps, I'd move up the eTrex product line a bit to get one that does WAAS.
Rugged and reliable. The XL flavor has an external antenna, which is essential for getting sufficient satellite signal in the deep wet redwood forests around here. This is a tough feature to find these days.
Fantastic user interface. Little things like displaying the datum along with the coordinates, and including the E and N to indicate easting and northing for UTM coordinates.
Garmin iQue 3600
Here I've broken all of my rules. It's pricey, and has maps and a big color display. My reason for buying this one is that it combines a Palm Pilot with a GPS, and is thus the first "all in one piece" GPS that I can write programs for. In my other life, I'm a software developer.
So I tried out the driving directions feature and was surprised to find it's actually useful. The voice guidance for turns is essential. Get it all set up before you leave. Don't even think of using the user interface while you're driving. But a skilled copilot can even locate a Starbucks on the route ahead using the built in yellow pages info. The copilot was me, the user interface was more complicated than my wife was willing to attempt.
Probably not. A basic GPS will do little more that report your current position as a geographic coordinate. You'll need to relate these coordinates to your position on a map and then decide how to navigate based on that.
It is however useful to recall that humans have been able to navigate successfully without maps and high tech gadgets for thousands of years. I've been working on how to teach people to navigate without such a reliance on gadgets. I'll put a link to this info once the page is up.
You will want to go into the setup menus for your GPS and look for menus like "Navigation" and "Position Format". You should find a menu that gives you choices like:
- USER UTM GRID
- hddd mm.mmm
- hddd mm ss.s
You want to select UTM/UPS.
Some other countries in out of the way parts of the world have used coordinate systems that are UTM like, but not lined up with the standard UTM zone scheme. By determining values for Longitude Origin, Scale, False Easting, and False Northing, the GPS can usually display these coordinate systems.
Your choices are...
hdd.ddddd - Decimal Degrees
hddd mm.mmm - Decimal Minutes
hddd mm ss.s - Degrees, Minutes, and Seconds
Outside influences usually decide this for you. For example what format does the guide book, web site, or program use? Does your team or group of friends use a particular format.
My own preference is to use decimal minutes (hddd mm.mmm), when nothing is pushing me to use something else.
This is usually a datum problem. Make sure that the datum used by the map is the same as the datum set in the GPS. In the continental US this will usually be either NAD27-CONUS , NAD83, or WGS84. NAD83 and WGS84 are equivalent for a practical purposes. See this link for more details.
10 - 20 meters (30 - 60 ft.) is typical, but there are a lot of variables. You should learn to check the GPS receiver's estimated position error value. Depending on the amount of sky visible, the configuration GPS satellites overhead and numerous other factors your accuracy at any given time could be much worse. (I've seen EPEs as high as 900m) With a WAAS capable receiver and a WAAS satellite in view you may get accuracies as good as a few meters.
You should consult the USGS Geographic Names Information System (GNIS) at http://geonames.usgs.gov/
Remember that a lat/lon coordinate defines a point on the earth. How you decide what point to use for something large like a city is up for interpretation, which is to say their may be many correct answers.
You have several options...
Here is a web site that will do it for you: http://jeeep.com/details/coord/
You can find software to do it using your computer. The best solution if you have lots of points to convert.
You can use you GPS unit:
Store the coordinates as a waypoint or landmark, switch the GPS to the desired coordinate system/datum, and recall the stored position.
MGRS is just a special format for describing UTM coordinates. So the simple answer is that they are the same coordinate system.
UTM coordinates are specified as Zone Number, Meters East (the easting), and Meters North (the northing).
MGRS uses a Zone, A 2 letter code to indicate a 100km square, and an easting and northing value. Then the numeric easting and northing are abbreviated. See this link for details.
The Zones are the same between the two systems, and the MGRS easting and northing values directly correspond to digits within the UTM easting and northings.
The grid line at the center of a zone, is the only one that is aligned with true north.
The UTM grid lines are aligned with true north at the center of each utm zone, which would have an easting value of 500km. As you move away from the central meridian, grid north, will vary a bit from true north. Most USGS topo maps will show the value for grid north (labeled GN) on their declination diagram. Usually it's less than a degree off of true north, and many folks ignore the difference and use the UTM grid lines as true north reference for plotting compass bearings.
If you put them into your GPS as waypoints/landmarks and add them to a route, your GPS will calculate the distance for you. Button pushing details are different for each GPS model, so that is left as an exercise for the reader.
If you have the points in UTM, and they are close enough together to ignore the curvature of the earth, you can work with them like XY Cartesian coordinates.
The old Pythagorean Theorem will let you calculate the distance like so
distance = sqrt( (X1-X2)**2 + (Y1-Y2)**2 )
Do a Google search on Pythagorean Theorem for prettier equations and pictures.
If you assume that the world is a sphere, then the distance between a degree of latitude (N-S) is constant where ever you are on the globe. The distance between a degree of longitude (E-W) varies from the equator to the poles. It is the same as the distance between a degree of latitude at the equator, but is zero at the poles. A very rough calculation is that
longitude distance = latitude distance X cos(latitude)
so if a minute latitude is 1.15 statute miles then at 38 deg 15 mins (38.25 deg) it would be
1.15 X cos(38.25) = 0.9031 statute miles
and at 38 deg 16 mins (38.266 deg) it would be
1.15 X cos(38.266) = 0.9029 statute miles
a difference of about a foot.
Of course since the world is really an ellipsoid, the actual calculations are more involved. The cosine approximation works well for large scale maps covering a small portion of the earth (like a 1:24,000 topo for example)
It is a false assumption that a coordinate value based on the 1927 North American Datum is less accurate than one based on NAD 83 or WGS 84. The coordinates for the same location are different. But given that the datum of the coordinate matches the datum used on the map, you will see no difference in the physical location.
By way of an analogy, imagine that a map maker had decided to express all "coordinates" on his map as the distance from the tip of the Washington Monument and another map maker had decided to use the top of the empire state building. Their "coordinates" for a given location would be different, but each map would still be an accurate representation of the area.
NAD 83 and WGS 84 are probably a better mathematical approximation of the shape of the earth than is NAD 27. If you wanted to do accurate calculations of distances and directions spanning large portions of the globe this might make a difference.
For the everyday GPS user using a handful of topo maps the important thing to do is to match the datum set in the GPS with the datum the map uses. Using the wrong datum can result in position errors of hundreds of meters.
UPS or Universal Polar Stereographic is used in the polar regions north of 84 deg. and south of 80 deg. It is based on a polar stereographic projection tangent at the pole. (Picture a radar scope centered on the north pole.)
From a users prospective it's still a square grid measured in meters. Should you end up in the poles, you'll find using UPS seems very much like using UTM.
Setting your Garmin to display UTM/UPS is what you want to do. It will switch between the UTM and UPS regions should you happen to wander into the polar realms.