This is Wahroonga Farm's attempt to demystify the world of GPS.
Copied by permission from GPS Australia Forums
Wahroonga Farm wrote:
How are maps sourced and made?
Almost all maps are initially sourced from calibrated paper or digital images.
A vector map maker starts with a paper or digital map in a particular scale. Roads, features pois etc are then converted to vector format. Digital maps are made up of many layers, each adding a particular layer of map features. These layers provide a convenient method for the map maker to utilise technology to do the conversion. However, any imperfections in the map will be transferred to the vector copy. Obviously the higher the resolution/ accuracy of the source map, then the higher the quality and accuracy of the vector map.
The OSM project is a significant exception. It is mostly sourced from actual GPS data captured by GPS enthusiasts.
Google maps is another which has undertaken large scale survey work. Although largely based on source map data, given the enormous effort that Google maps has expended in 'on the ground' mapping and street level photography, one could suspect that Google map quality and accuracy increasingly benefits from this 'on the ground' survey work.
Sensis and Navteq, the two major Australian street navigation vector map makers, both claim on the ground survey teams which work to improve accuracy, however in my opinion, they're efforts are not on the scale of OSM and Google.
A Vector Map Example
Shonky Logics' maps are generated from an earlier GeoScience Natmap 250k map. It is licensed for non-commercial use. All of the features of the 250k map were faithfully converted to vector format. Additional information improves the map detail particularly for 'water related' features.
You can view the Natmap 250k in OziExplorer (raster) or Shonky in Mapsource (vector) and yes ... they are identical.
However as you zoom in the raster map, the images blur, whilst zooming in the vector map, maintains sharp images. Since the source data is 250k, zooming greater than that best viewed in Ozi will simply increase the error margin when in Mapsource.
Perhaps a few pictures can help illustrate this effect. These series of pictures compare Shonkys' Garmin vector maps against their GeoScience raster map source. The two map views displayed below are PC images taken from Mapsource -Vector and OziExplorer - Raster.
The area chosen is the tip of Cape York, Queensland
Mapsource at 15 Km zoom
Ozi at an equivalent zoom Compare the detail. Raster maps win out here.
MapSource at 3Km zoom
Ozi at an equivalant zoom Compare the detail. It's pretty much the same. In my opinion 'raster' gives the clearest view of the map and features at this zoom level.
Mapsource at 700m zoom. Vector maps come into there own now, however beware mapping errors which become magnified.
Ozi at an equivalent zoom. Notice the fuzz has set in. Not too good and you would probably not operate for long at this zoom level.
