There was a story last week about counterfeit GPS maps causing drivers to get lost in Shanghai, which was widely reported in mapping blogs (like GeoCarta and The Map Room) and discussion groups. But what do they mean by counterfeit maps? Jesse at Very Spatial started to address this, saying "I disagree with their use of the word ‘fake’, inaccurate is more realistic." You can make custom maps for your GPS that may be sloppy or deceptive, or they may be more accurate than what you can buy commercially.
Let’s take a look at how this is done. What follows is a brief overview of a subject covered in great detail in my book, GPS Mapping – Make Your Own Maps, which includes step-by-step instructions.
Why would you want to do this? Well, you might be traveling to a foreign country for which there are no good GPS maps. Or you might just want better topo maps than what is available commercially. This is a common problem for outdoor recreation enthusiasts, as almost all GPS maps are based on 1:100K scale data, the one exception being Garmin’s US Topo 24K series (Amazon), which only covers national parks. Garmin’s US wide product (Amazon) shows contour lines 130 feet apart. I don’t know about you, but I like to know if I’m about to ride my mountain bike off a 100′ cliff! And while the Magellan (Amazon) and Lowrance products show contour lines much closer together, they actually interpolate the 1:100K data to do so, which is misleading to say the least.
On to how to make custom GPS maps…
The first thing you have to do is obtain your data and convert it to the proper format. We’re talking vector data here, not scanned (raster) maps. Map data can consist of GIS file types such as shapefiles, or info like digital line graphics (DLG’s) from USGS or other sources. From there, you just need to get it into your GPS. There are different techniques for different brands…
Perhaps the most popular method for Garmin relies on cGPSmapper. An excellent resource for these techniques re: Garmin units is the Yahoo Map Authors discussion board. And despite what you may read, this can be done without registry hacks or tracing contour lines. It’s all covered in my book, as is the process for Magellan and Lowrance.
As much as I love Garmin, I have to say that the process of loading the maps into a Magellan is much easier, thanks to their free MobileMapper Office software. The best web reference on the process is the Yahoo MobileMapper2 group.
Unfortunately, it’s been a while since you could hack a Lowrance map. Folks with MapCreate version 4 could do it, but we’re now up to version 6.3. There is a solution available to Lowrance users though, as their mapping units tend to have extensive track memory, allowing you to layer roads, contours, etc., as tracks. UPDATE: You now have more options for creating custom maps for Lowrance GPS receivers.
A caveat on routing
Making maps is one thing. Making them "routable," allowing for turn-by-turn directions on roads, is another thing entirely. Maybe that’s where the Shanghai hackers ran into trouble.