Maps and Global Positioning System

Maps and latitude and longitude data for global positioning system GPS receivers.

Global Positioning System Background

NAVISTAR (Navigational Satellite Timing and Ranging) was developed and deployed by the US Department of Defence, with the first satellite in 1978, but not declared fully operational until 1995. It uses 24 (plus some spares) satellites circling earth every 12 hours, in six orbital strings of four satellites, so as many as eight can be spotted at any time.

The satellites contain four atomic clocks, accurate to about a nanosecond. The transmitter output is around 50 Watts. They transmit two L band carriers. L1 at 1575.42 MHz is uniquely modulated using a 1.023 MHz PRN (pseudo ramdom noise) code with navigation message and course information. The 1023 bit or 1mS signal repeats and is the old civilian navigation signal. L2 at 1227.6 MHz carries (optionally encrypted) precise positioning for military use. The navigation information in a 50 Hz signal contains almanac data which roughly estimates the satellite position. It takes about twelve minutes to download the almanac and ephemeris data when you first turn on a GPS receiver.

GPS receivers calculate the distance to multiple satellites. The GPS receiver generates an identical PRN signal, compares the two, and determines how much delay is needed to match signals. This gives a distance estimate. Three such measurements would determine position, however the GPS receiver does not have an accurate clock (1mS error is over 300 km). They take a measurement from a fourth satellite, and adjust the receive clock until the distances of the four satellites pass the same point. Solving four simultaneous equations in four unknowns give the position, and time. Errors occur because of epemeris errors, atmospheric conditions, multipath signals, but the biggest error has always been that until May 2000, errors were deliberately introduced into the satellite time signals.

There is a good reference by Peter H Dana at

GPS Latitude and Longitude or Map Data Sites

Australian Geographical Placenames (Gazetteer)
Search on a place name to obtain a report including place name, state, place type (town, mountain etc), Latitude and Longitude in degrees, minutes and seconds (and in decimal degrees), 1:100,000 Map Sheet Code and 1:250,000 Map Sheet Code. You can also generate a map, showing the position in Australia, and a locality map covering about 300 km around the area. This site is great for working out precisely which maps you need to include a specific area. Formerly
SwopNet Waypoint Database
A listing of waypoint databases, said to be the most complete on the web. Also links to much general material about GPS and related topics. Very handy site. They listed five sites for Australia and NZ, but three are small areas, and one used script code that didn't work with any browser I use, so it was unviewable. The only good one was the Australian Gazetteer above. Formerly

Map Sites - Australia

This is the Australian government mapping authority, Australian Surveying and Land Information Group, at the Department of Industry, Science and Resources. They have a lot of land use data for sale, but the most interesting (and cheapest) one for personal purposes seems to me Australia Unfolded 2. This is an interactive atlas that lets you design and print your own maps. It is derived from their 1:250,000 scale topographic maps data. The A$70 CD provides 288 Mb of vector data and 175 Mb of images in TIFF format. Maps can be saved as Windows bit maps (BMP) format, for conversion to Epoc MBM. I don't as yet have a good method of extracting the map vector data. Formerly
Auslig Map project
There is a nice map of Australia in JPG format at Auslig. This comes with four sets of 35 thumbnails (NE, SE, NW, SW) so you can select the maps you want. The whole of Australia is covered, broken down into 140 map sheets. These larger scale map (about 100k download each) sheets can be obtained by going into the directory big, and selecting the four master html files. Be warned, a 3 MB download over the phone line takes time, and your browser must be capable of saving all the 35 map graphics in one move. You may need to pay for access now. Formerly
Coastline Extractor
You can download vector data to create outline maps for coastlines. Sizes up to 500,000 data points (don't do more than a few degrees at a time). Program tried to produce an html file pointing you at the generated data file (in /tmp) but this appears as a .pl file and so the browser doesn't display it (access by listing the contents of the .pl file, then point your browser manually at the generated data file). Great for islands. I got some nice outlines of the Whitsundays from them. Use - for south, and east is +. This is a USA site, but seems to have coastline data for the entire world. Formerly but try
Hema Maps
Maps and guides for touring and four wheel driving in Australia and New Zealand. Their Atlas of Australia on CD-Rom is also available around A$70. I tried converting some images for the Psion, and got reasonable results. Better software for doing the conversion from a colour Windows bitmap to a grayscale would help a lot. Really need to be able to use larger grabs than you can get into the Windows clipboard (something like 1500 to 2500 would be much better). Certainly better than having nothing however (their paper maps are fine!)
Map Centre, Parramatta
Very helpful map shop in North Parramatta, NSW. We picked up a nice 4Wheel Drive book there in 1999, and will certainly visit again when next in the area. 440 Church Street (Crn Grose St) Phone (02) 9890 2080
They do computer maps of Sydney and Melbourne based on Melways and Sydways for GPS use. The more general moving map software for Windows is called Fugawi and costs A$150. They also have a moving map software called NeverLost at A$95. You can get a bunch of the maps on CD, but the price of all the Auslig stuff is pretty steep for amateur use.
Map shop where US readers can buy maps of Australia, described in an extensive catalog which also lists major mapping authorities in Australia.
Map Maker
University site on maps and geographical information systems. Formerly

Map Sites - World

Global Gazetteer
Information plus latitude and longitude for places all over world. Fast and efficiently set up. Over 2 million towns, 19,000 in Australia. Generates an excellent map, and links with Google. Their generated maps appear to use bulk topographic data, and overlay a coastline. Very effective, and a real handy site. Includes airport weather. Coastal map database from GMT system, from University of Hawaii. Terrain information is GTOPO30 (30 arc seconds or about a square kilometre per data point). Formerly
Choices World
Lots of material about free maps, with good links to UK and USA maps. Alas, Australian maps are scarce as usual. Formerly
Garmin MapSource
Maps for Garmin GPS receivers
Joe and Jack's GPS
A really nice site with excellent pointers to many other sources of GPS material. Formerly
The Mining Company (
They check the quality of the sites they list, which makes them a very handy resource when they have appropriate material. Their material about finding Australian maps formerly starts at
Omni Resources
An international map specialist. They have a good variety of paper maps of Australia, and access to digital data.
Street Map UK Does streetmaps of given locations.

Map Sites - Mostly USA

Check Open Directory Maps
Look up USA streets on and punch the coordinates in on your GPS. Mapblast does street level coverage for US. US also has house numbering. Does not appear to do outside the USA, although I heard reports it did. Display was far too busy with spam. Formerly
General USA maps, and I thought it easier to use than Mapblast. Display was far too busy with spam, however you could extract helpful street level maps of areas centered on a hotel.
Generates driving directions from one place to another for USA and Canada, as well as maps. Display was far too busy with spam.
National Geographic
Some hi res downloadable maps on their map machine.
NOAA MapFinder
NOAA's MapFinder site. Too slow to test (didn't even get the first page up) , but reputed to have some good material.
Tiger Mapping Service
A USA only digital map database, produces public domain GIF images of map data from their data. Designed by Chris Struber for US Census Bureau. Worked very fast when I checked it. Their credits page gives pointers to map data manipulation programs and sources of US map data. No longer seem to have funding for this wonderful resource.
University of Texas
Perry-Castaneda library site with many varieties of maps, relief, political, historical. Good for current events.

Mapping Software - General

PC map software
OziExplorer and GPSUtilty can display Lat/Long, UTM, OSGB and others. Probably for Windows 9x. No other details.
I hope you have enjoyed