General Questions

Questions about geographic coordinate systems

Questions about GPS selection, setup and use

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General Questions

Questions about geographic coordinate systems

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.

Some of the reasons I like to do my own declination correction... No sighting compass can be adjusted for declination. I like using a sighting compass. There is no need to check my compass to see if it is adjusted correctly. It always gives me a magnetic bearing. A mis-adjusted compass give a bearing related to some random number. Hard to go back and correct any past data if you don't know what the mis adjustment was. This is a bigger problem with the Brunton compasses where the adjustment is a friction fit. Once the compass has seen some wear, there tend to adjust on their own. Because I think about declination every time I move a bearing between my compass and my map, I am more likely to have thought about what the current declination is for my current location, and I'm more likely to remember what declination is and how it works. I run across way too many people that have either forgotten how and why they adjusted their compass, or worse they had someone else do it for them. They don't understand declination. Sometimes they can't tell me if their compass bearing is relative to magnetic, true or grid north. The often have an incorrect declination setting for their current location. The downside of my choice is that I have to think and do some simple addition or subtraction every time I move a bearing between map and compass. I have talked with some extreme adventure racers that feel they are operating so close to the edge of physical and mental exhaustion, that they have no business doing any thinking and want their compass to do the correction for them.

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 mapmaker had decided to express all "coordinates" on his map as the distance from the tip of the Washington Monument and another mapmaker 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.

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)

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.

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 500 km. 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.

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.

You have several options...

Here is a web site that will do it for you:

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.

You should consult the USGS Geographic Names Information System (GNIS) at

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.

Questions about GPS selection, setup and use

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.

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.

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, website, 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.

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.

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:

hddd mm.mmm
hddd mm ss.s

You want to select UTM/UPS.

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.

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...

Garmin eTrex
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.

Garmin 12XL
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.

Magellan Map330
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.

MapTools and our products

Free downloadable tools

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.

Web tutorials and exercises

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.

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 i s not visible as the base of your coordinate measurement.

Using our products

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.

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.

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.

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.

The 30 mil plastic stock is similar to a credit card in both thickness and flexibility. You can bend the tools in half, without breaking them. When you unbend the tool, you'll have an ugly white crease mark, but the tool will most likely still be usable.

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.

Purchasing our products

Yes. We do a great deal of business with federal, state and local government agencies and are happy to accommodate your particular agency's purchasing requirements.

Our online shopping cart will accept orders using government credit cards or purchase order numbers. Federal government end users in California can request an exemption from sales tax during the checkout process. We don't charge sales tax for orders that ship outside of California.

If you need a formal written quote, you can either call or email us, or you can place an online order with the PO number of "Quote". We'll review the order and email you a quote.

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.

I've also been downloading maps from the folks at Their maps are free and can be downloaded as a pdf file.

We don't have a retail store. We do have a warehouse and production facility in San Carlos, CA. If you are local, you can come and get tools directly from us. Please make prior arrangements, so that we can be sure to be here.  We do things like taking off for a hike or to go work out at the gym in the middle of the day, so there is not someone at the warehouse during predictable hours.

We have a handful of retailers that carry our products in their brick-and-mortar and/or online stores. See our Dealer List for a current listing. 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.

Yes. You can give us a call at (650) 332-7522. John is currently the only person that answers the phone. My hours are generally M-F, 9am to 5pm pacific time. But I am frequently away from the phone so you will likely need to leave a message.

But let me try and talk you out of calling to place an order. When you call, and I actually answer, I'll likely be on my cell phone. I might be out on the production floor, in a meeting, running an errand, at the gym, or on a hike. I'll find a scrap of paper and take down your order information, and stuff it into my pocket. Really, we do not have agents standing by. This is low tech, and only somewhat secure and reliable. But it's how lots of tiny scrappy businesses like ours run.

You should at least place your order on the internet. You can still choose the payment option for calling your credit card in by phone.

If you do put your credit card information in on out web based shopping cart. It first gets encrypted right in the web browser on your computer. Then it gets sent over an encrypted link to our credit card processing company, where they can afford the top-gun security guys to keep it safe. Here at MapTools, we never have your credit card info, we just get a token that allows only us to charge the amount of the order, or to issue a refund up to the amount of your order.

So it's up to you to decide. You can use what I just described with our secure shopping cart, or your credit card info can live on a slip of paper in my pocket, or on my desk, until it gets sent to our credit card processor using my computer instead of yours. I do promise to either shred or eat the slip of paper once I'm finished getting it into the computer.

Still worried? You can mail us an order, using a money order for payment. Best to pay for the money order using cash.

Our complete product line is available on our web site,

You can also get a list of our products sorted by map scale at,

We also sell many of our products through

We have a handful of retailers that carry our products in their brick-and-mortar and/or online stores. See our Dealer List for a current listing. 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.

About your order

Where is my order?

We'll try hard to make sure it does. But you need to let us know that you need it by a specific date. At the very least add a note to your order when you checkout. If time is short, it's best to call or email so that we can figure out the best delivery option without having to spend way too much money on shipping.

Send us an email at, remember to include your order number.

Several things may have occurred:

  • Your order was lost by the Post Office.
  • We had a problem processing your order and you didn't get or didn't respond to our email inquiry.
  • You gave us an address that the Post Office could not deliver to. In which case your order is likely on its way back to us.
  • You are too optimistic on the time it should take to arrive, and just need to wait a bit. Despite their motto about snow, sleet and hail, bad weather and other natural disasters do delay the delivery of the mail. Sometimes it takes a bit longer than we both think it should.
  • And yes on rare occasions our computers burp and loose an order completely.

Once we get your email, will sort out what we think should have happened. You can save another cycle of email back and forth by confirming your shipping address in your first email.

When we're sure we have the right address, and it really should have arrived by now, we'll reship your order.

We do ask that if you happen to receive two shipments, that you return the second one to us. This is easy, just cross out your address, and write "Return to Sender" on the shipment, and give it back to the Post Office folks.

Our computer system will send you and email to confirm that we received your order, and again when we ship your order. Both emails will be addressed from

If you don't get these emails, it is most likely because a spam filter somewhere between our computer and yours decided the email was spam and filtered it. It may be sitting in your Spam or Junk mail folders. Since we are a tiny business most spam filters don't "learn" that our customers really do want our emails.

Occasionally our customers enter their email incorrectly and it will fail to be delivered.

You can always email us at to inquire about your order. Please include your order number. We'll do our best to get a quick answer to you regarding the status of your order.

Most of our orders are small, flat, and weigh under 13 ounces. This makes USPS First Class Mail the lowest cost reliable shipping option.

Orders are shipped from San Carlos, California 94070.

Most orders ship in a flat brown 6"x9" envelope and will be delivered along with the rest of your first class mail. These first class mail envelopes are not trackable. Once they have been mailed we can not get any information about them unless they get returned to us by the Post Office because they were undeliverable.

Our web site offers Priority Mail and Express Mail as faster and more costly shipping options, both of which are trackable. We have to have Express Mail shipments to the Post Office by 3pm pacific time, if we want their delivery commitments for that day.

Orders that are placed through and shipped by MapTools are shipped the same way the rest of our orders are, with one exception. Amazon pushes us really hard to provide tracking information for shipments. So we charge a bit more for these orders and ship them as a First Class Package, which unlike the envelopes is trackable. Overall this has been working really well, but there are a few postal clerks out there that are not up to speed on the First Class Package rules, and return them to us with the explanation that First Class Letters and Flats are not eligible for tracking.

We can also ship using UPS and FedEx. But our shopping cart will not offer those options yet. So you need to call or email if you need that sort of shipping. We're working on a better shopping cart. But progress is slow.

We ship most of our orders on the same business day we receive them. We ship Monday through Friday, with holidays on pretty much the same days the US Post Office has holidays scheduled. The postal carrier picks our mail up sometime between 10 am and 3pm pacific time. When orders are ready to ship after our postal carrier has come by, we take often take the envelopes to the corner mailbox just before 5pm when its contents get picked up. Packages usually have to wait to the next day.