Digital Mapping Basics

GPS equipment can be a lot of fun. Finding out where you are, or sharing your trips with others, adds a whole new dimension to traveling. Most of the time, it's easy. You take the software that came with your GPS, download the tracks, and share them with other people. However, problems can creep in when that sharing starts. What if they don't have the same type of GPS or software? Why does that track you downloaded from the web not show up on the map where it's suppose to? This post is the first in a series to help explain how to take your digital mapping to the next level, or at least to help explain why your downloaded hiking track shows up in the middle of the ocean. The series starts with some digital mapping fundamentals before getting into some available software, and the technical details of conversion.

Digital Mapping Fundamentals:

The first thing you have to understand about digital maps is that there are fundamentally two different kinds: raster and vector. A raster is just like a digital picture, or your monitor for that matter. A raster image is just an array of dots, across and down, where each dot can be a particular colour. If you want to draw a line, you just turn the dots on from point A to point B, and it looks like a line. The pictures you take with your digital camera are raster images. Vector images are different. A vector image is actually a collections of lines, polygons, or points that are listed as descriptions, such as: line, starting at 50x80, ending at 230x100, thickness 2, color green. The computer program then takes than information and calculates what you should see on your monitor. Now, the end result is always the raster image on your computer monitor, but the underlying data can be raster or vector. Vector data is very important to digital mapping. I don't want to get lost in a lot of technical details here, so if this isn't clear, try reading Graphic File Types for more background information.

Vector data is a collection of points, lines, and polygons. A point is pretty obvious. Just like a graph, a point is just a dot at a particular X and Y coordinate. A line is also pretty simple, it's just a straight line between two dots, though it can be extended to be a whole bunch of straight lines strung between a series of dots, one segment after the other. When a group of line segments, a minimum of three for obvious reasons, closes such that it begins where it ends, then it can be a polygon. Think of a polygon as a shape that has a center. It doesn't have to be geometrically nice, like a square or circle, it just has to have a continuous border that encompasses a center. In mapping, polygons are used to outline things like lakes, so they may have hundreds of short little line segments to define the shoreline.

Another interesting point about vector data is that, if the data is set up properly and the software can use it, it can allow routing. Routing is where you pick a place on the map and ask the computer to draw out a route that follows the roads in the maps. Most any mapping software can make routes from point to point, but only routing vector maps will allow the route to actually follow the curves of the roads, between the points.

The second thing you have to understand is that digital map data must be georeferenced to be useful. Georeferrencing is when you place particular raster images or vector data at particular places within your geographic framework. For example, a georeferrenced raster image may have its top-left corner set to one lat/long coordinate and the bottom-right set to another. Thus, mapping software can then "know" where that image is and place other data with it accordingly. This is the important point here: georeferencing allows you to combine different sets of map data together, so long as they have the same referencing system. If you had two raster images, properly georeferenced, you could bring them both up in the same mapping application and they will be displayed in the correct orientation, side by side for example. Alternatively, and this is the most common situation, you could have vector mapping data, a downloaded track from a GPS for example, overlayed on top of a raster image for a particular area. If everything is georeferenced properly, and all the data shares the same reference system, the vector and raster data should line up. Your track will go down the road.

Now, this is where digital mapping gets weird and difficult. The wonderful thing about geographic "references" is that there are so many to chose from. For two sets of mapping data to line up, they must have the same coordinate system, and the same projection, and the same datum, and the same spheroid. So, lets work through these one at a time:
  • The coordinate system is what the map data is measured in. Most nautical maps are in latitude and longitude. Hiking maps are often in UTM meters. But, even with this limited sample, things get more confusing, lat/long maps may be recorded in decimal degrees, or degrees-minutes-seconds or even a combination of those. UTM, or Universal Transverse Mercator, is not so simple either, what with the regions and all. So, the first thing to do when combining map data is to make sure all the data is using the same coordinate system.
  • A map projection is, to put it simply, how the map is distorted to represent a curved earth on a flat screen or paper. Anyone that has compared a paper map of Canada to a globe will have noted that Greenland, and the north in general, appears much bigger on the paper map. This is because paper maps distort the north, usually in the "Albers" projection. The alternative is to get those flattened "orange peel" maps. Hiking maps, because they are usually of much smaller scale, don't have to deal with as much distortion, so UTM works better. There are lots and lots of different projection systems out there. Albers and UTM are just a couple of the more common ones.
  • The map datum is where all the measurements are referenced from. Again, there are lots to chose from. The GPS world has, thankfully, standardised on the WGS84 datum. The Canadian 50k topographic hiking maps use NAD27. So, if you take your GPS and read off a nice UTM coordinate, then look it up on a paper hiking map, you will find that it's telling you that you are not where you really are, you will be off by almost a kilometer. To correct this, you will have to go into the settings of your GPS and set the display datum to match your paper map. Again, if you are going to combine mapping data, you have to make sure they are using the same reference or you won't get what you expect.
  • A spheroid is the mathematical model the mapping software uses to calculate how the earth curves. This is not quite as simple as you might think; the earth is not actually round. Thankfully, this really isn't too big a deal when dealing with small-scale maps, so you don't generally have to worry about it. It can become important if you are converting mapping data from different sources as an incorrect spheroid setting may shift the calculations, and thus your data, off by enough to be noticeable. But, for most of us, it doesn't factor in that much.

If you look at a paper map, or the "meta data" that is suppose to come with all your digital mapping information, it should list off all of this information: coordinate system, projection, datum, and spheroid. If you want to combine data sets, then make sure they are compatible, or that your mapping software can either convert or combine them on the fly.

The third thing to understand is that not displaying information is also important. If you tried to display all the information in your mapping data at the same time, all the time, then when you zoom in or out you would either have a lot of blank nothing at maximum zoom or a solid mass of gibberish at minimum zoom. Think of it this way, if you put all the information available on the 50k topographic maps onto the 250k topographic maps, then the 250k maps would be a useless mess. There are two map series for a reason, the 250k maps show much less detail but a much larger area. The two map series are, in a manner of speaking, two different zoom levels. Similarly, mapping software, either on your computer or on the GPS, must show different levels of detail depending on what zoom level you specify. Most GPS systems will have a "detail" level that controls this, to some extent, as does most computer mapping software. However, much of what is displayed, or not, is the choice of the cartographers that made the maps in the first place.

Cartography is as much an art as it is a science. Maps are not a pure representation of physical reality. Information is included, or excluded, emphasised or minimalised, as the cartographers see fit. If you start working with raw digital mapping data, you will quickly realise how important these decisions are to creating good looking, useful maps. Like photography, and so many other things, computers are spreading out the specialised tools of cartography to the general population. Anyone can start making maps now. However, like photography, don't expect world-class results without a lot of work.


Converting Google Earth KML files To Other Mapping Formats

Here's a tutorial on how to convert the tracks you can download here to other mapping formats, including Garmin. It's actually very easy to do, with the right tool.

To get the right tool, go to www.GPSbabel.org and download the GPSbabel tool. Just follow the "downloads" link on the left hand side. Pick the file for your computer, DMG for Mac or Zip for Windows, and download to your computer.

Oh, and if you share my inability to spell, it's GPSbabel, not GPSbable.

There are too many variables for me to describe exactly how to install in every possible situation, but if you're running WinXP or OSX, you should just be able to double-click the downloaded file, then go into the folder that opens and double-click the application. If this doesn't work, then I suggest you back up and read the documentation on the GPSbabel site. If you still have install problems then leave a comment with your particulars and I'll try to help.

GPSbabel converts tracks and waypoints between mapping formats, lots and lots of different formats. Think babel-fish in the Hitchhikers Guide to the Galaxy series, but then if you understand this reference you're probably so much of a geek that you don't need this tutorial :)

Anyway, with GPSbabel running, just pick the file format you want to start with, browse to the actual file, pick the file format you want to finish with, and hit "Save File" - that's it. Oh, don't forget to pick what you wanted translated: points, tracks, or routes. Supposedly, it can even send and receive files directly to many different GPS receivers, though I've not tried this.

Personally, I use an older less-crippled lite version of OziExplorer for communication with my GPS. I have Garmin's Mapsource but I never use it for tracks or waypoints, basically because it's pretty substandard compared with Ozi. I recognise that many people don't use Ozi so I'm also converting and uploading to Google Earth KML format.

So, to use the tracks I have available for download:
  1. Follow the blog links here to get to the KML files.
  2. Download the file. If you use IE (which I don't recommend) you will have to right-click on the KML file and choose "save target as."
  3. If you have Google Earth installed (which I do recommend) you can then double-click on the downloaded KML file and it should open in Google Earth.
  4. If the track looks interesting to you, then continue through with the conversion.
  5. Start GPSbabel.
  6. Browse to the KML file. It should automatically change the input file type to Google Earth.
  7. Choose your output type or just select your GPS receiver.
  8. Either hit "Save File" or "Send GPS", depending on what you selected.
And that's it.

If you have any questions about this then leave a comment. I'll do my best to help out,


Download links: GPSbabel, OziExplorer, Google Earth

NOTE: the KML track problem should be fixed (Thanks to David for pointing this out)


More Vancouver Island Tracks for Download


I've posted another couple of tracks for download, both in Google Earth KML and OziExplorer PLT:

  • All the major powerline routes on Vancouver Island.
    A detailed description is HERE.
    The track is HERE.

  • A bush camping spot on the San Juan river, near Port Renfrew, Vancouver Island.
    A detailed description is HERE.
    The track is HERE.
Enjoy, and don't forget to leave some feedback if you download a track... I'm starting to wonder if I'm doing all this but nobody really wants to know.



Route: Renfrew to Skutz Falls

Here's a section of the VMC 2006 Canada Day Dualsport race. It goes from Port Renfrew up to Skutz Falls. Parts of it are active logging road, even on Sundays, so be careful. Other parts include some really nice sections of single track.

All in all, it make a good back-route dualsport connector between the Sooke-Renfrew and the Cowichan Lake areas. There's a main road you can follow instead - but it's basically improved gravel - pretty boring on a dualsport, in my opinion.

You can download the tracks in Google Earth or OziExplorer formats HERE.

More tracks are available HERE.


50K Topograhical Maps of Vancouver Island

Update... This data can now be found at: Geogratis, in their CanMatrix area. It looks like the Free side won the argument. Everything you can image is now available for easy download, for free.

The rest of this is old news...

The Canadian government prints a lot of maps, including the standard 50K topographical series that most of us grew up with. For a while, there was a government website, called Toporama, where you could download these as large GIFs - available royalty free, even for commercial use.

When I first found this site, three things struck me:
  1. the maps were amazing.
  2. the interface was pathetic. It took forever to find and download a map.
  3. the file structure on the site was very well organised.
So, I whipped up a simple Perl script to grab all the maps for Vancouver Island, all 200 of them, from this very orderly file structure.

The Toporama site has been replaced by a new government server that offers online maps through what amounts to a GIS interface, but the ability to download the 50K maps seems to be gone. However, the original Toporama site is still operational, though I can't find any obvious links to still download the maps.

But, the big surprise is that the maps are still on the server, and you can still download them. Personally, I don't really care... I've downloaded all I want a long time ago. But, I thought other people might be interested, so...

I've created a download page HERE with links to each individual file, at least for Vancouver Island. Get them while you can because I suspect they will disappear at some point.

You can go here to find out which maps cover the area you're interested in.

Here's a small sample of one of the maps available. You should be able to click on it to see the actual resolution.

Here's how they can look after being processed in Ozi Explorer at 50% and 25% zoom.

Rumour has it (and this is just rumour - no facts involved), there is a serious argument going on between two groups of people responsible for government cartography in Canada. One group wants all the data to be publicly accessible while the other groups wants to sell the information. I don't know if this is true, but it sure looks that way when you see how data appears and disappears. Over the last few years, I've collected about 8Gb of mapping data from government FTP servers, and Toporama. Availability seems to come and go; lately, the web-GIS systems seem to be taking over.

I don't like the web-GIS sites because I want the data on my drive, in my applications, where I can mess with it the way I like. Most of the time, I'm in Ozi Explorer with a set of 50K topos that I put together. With my GPS, they make a good combination, better than Garmin's mapsource or anything else I've tried, including ArcView.

Note: the above maps are a derivative work from these 50K topos, as such, I have to say:
"© Her Majesty the Queen in Right of Canada, Department of Natural Resources. All rights reserved." This means that they own the original data, but I own the derivative. These maps are available for commercial use, for free! Here's a link to the full license agreement.


Points of Note: Afghanistan, Kandahar Province, Panjwayi District

Here's a Google Earth file that highlights a few places of note in Afghanistan, Kandahar province, Panjwayi district. Basically, I've taken THIS map and georeferenced it in Ozi Explorer. From there, I marked a few waypoints of interest and converted them to Google Earth format. Because the source is a PDF file and, probably, the projection is off, some points don't exactly line up with the satellite images, but it's close enough to at least get an idea of where things are going on. The PDF map has a lot of names on it, and it's searchable, but it appears that various people can't decide on how the western spelling of Afghan names should go. So, it can be frustrating to figure out exactly where people are talking about.

When new place names come up in the news, and if I have time, I'll update the Google Earth file. Note: the file does have a bunch of numbered points. These are just road intersections that I marked as they show roughly how far the map is off in an given area. They don't mean anything else.

You can download the Google Earth KML file HERE

Place of note:

HAWZ-E MAD - Hawz-e Madad, the village where Canadian forces have been conducting Operation Baaz Tsuka. The area south of this is where the Taliban were reported to be holed up. While the village itself is pretty low-res in Google Earth, the area south of that is very detailed.

Other interesting PDF maps of Afghanistan are here:





Similar Posts are listed HERE


A few More Routes on Vancouver Island

I've uploaded a few more tracks I've collected over the last while.

Cowichan Powerline Connector:
A short connector between two rural roads - perfect for dualsporting

Jordan River to Port Renfrew:
The hard way - as run on the 2006 VMC Dualsport Enduro

Mnt Prevost:
North of Duncan, forest service roads.

Old Baldy Mnt:
A lookout by Shawnigan Lake - nice view from the top.

Have fun!

Don't forget to read the DISCLAIMER

Check out all the routes and waypoints HERE

Route from Port Alberni to Horn Lake

This route is only one way of many, I'm sure; there are lots of trails all around the place. I made this route on my KLR650 dualsport, with my girlfriend and camping gear, so it's not particularly difficult. At least, in the summer of 2006 it wasn't difficult: times change. Note that there are a couple of gates to go around, but both had well-worn trails around. There are some benefits to riding a bike.


Download the tracks in Google Earth or Ozi Explorer formats.

Other routes are HERE

Route to Labour Day Lake

Here's a route to Labour Day Lake, from the summit of the Alberni highway down through some 4x4 grade logging roads (as of the summer of 2006) and up to a parking area, sort of. The actual lake is about another kilometre or so down a hiking trail.

It is available for download in both Google Earth and Ozi Explorer formats.

Be sure to read the DISCLAIMER as well.

SIMILAR FILES are available. A detailed ride report is HERE