How Accurate Is Map Software?

[+MDAgent]

PC Map software identifies coordinates by some sort of algorithm, I suppose, using professionally surveyed known coordinates for reference.

 

How accurate are they, in general. The maps need to be drawn correctly, the reference points have to be correct and the 30,000 guys who entered all the data must not have left out a decimal.

 

What, in your opinion, is the reliability of your PC map software?

[+New England n00b]

Don't forget staleness of the data - new housing developments, roads... when was the last data sampling taken?

[+JohnnyVegas]

No maps are perfect, paper or on CD.

[+jimmyreno]

most of the benchmarks that are used for marking property rights are off by a hundred feet or more (my experience).

 

Considering that land is worth trillions of dollars in the US,

I'd think they'd be more accurate.

[+Night Stalker]

Most of the streets in my home town seem to be correct except of course mine. It is off about 100 feet to the west of where it actually is so when I drive down the street my GPS shows me driving through all of the homes on the east side of the street. Magellan and Garmin must use the same source for their maps because I had the same problem with my Magellan SporTrak Pro.

 

[+briansnat]

They're accurate enough to get you around. Not perfect, but I've not encountered any major flaws.

[+StarBrand]

Other than a very few slightly misplaced roads, all newer roads missing and the occasional misspelling - the products I have used have proven to be accurate enough for what I want and need. Certainly as good as any paper map I have seen.

[+welch]

I wouldn't let a computer drive my car with it, but overall its good.

[+AtoZ]

How do you define accuracy????

I placed a cache one near a street corner, about 50 feet from the road on either side. Took I thought a GPSr reading and went home to submit the cache. Well the GPSr freaked out or I couldn't read it and it had been still aquiring a signal when I marked the point, anyway I didnt have the waypoint. So I used my mapping software to get the lat long. The first two cachers said the coords put them in the middle of the busy intersection. Since then I do not trust mapping software vary much but to just get a general idea.

cheers

[dsandbro]

Roads are notoriously off. That's a function of trying to get as much detail as possible without making the map file size so large it is unusable. Roads are generalized. Zoom in close -- a nice smooth S curve on the ground will look 'angular' like a series of straight lines on the map.

[+G-Squad]

I purchased Magellan Mapsend in 2002. By then, I believe it was already 2 years old. The information on it was at least 4 years old when it was put out. So, by the time I got it, it was 6 years old...now going on 9 or 10 years old. The accuracy of what roads are on there is fine. It get's me from point A to point B without any issues. But, the problem is if the location of point A or B even existed back then.

[+MDAgent]

How do you define accuracy????

I placed a cache one near a street corner, about 50 feet from the road on either side. Took I thought a GPSr reading and went home to submit the cache. Well the GPSr freaked out or I couldn't read it and it had been still aquiring a signal when I marked the point, anyway I didnt have the waypoint. So I used my mapping software to get the lat long. The first two cachers said the coords put them in the middle of the busy intersection. Since then I do not trust mapping software vary much but to just get a general idea.

cheers

This is the root of my question. Is any map software accurate enough to use to place a cache, the way you did? The answer, everyone seems to agree, is no.

[+StarBrand]

This is the root of my question. Is any map software accurate enough to use to place a cache

Not that I have used - error margin is a bit higher than our GPSr errors.

[TCE]

I agree, I wouldn't let my car use it to drive by, or I'd drive through all the houses on mainstreet!!! Yeah, the basemap in my Legend is off by about a hundred feet on the main street going through town...but other than that, the major interstates, are pretty ok.

 

So far the coordinates are far more accurate than anything on the basemap...but maybe that's why it's called a "base" map?

 

Anyway, the maps are pretty good...but I wouldn't bet my life on 'em.

[+blindleader]

most of the benchmarks that are used for marking property rights are off by a hundred feet or more (my experience).

 

Considering that land is worth trillions of dollars in the US,

I'd think they'd be more accurate.

This is a bit off topic, but since you brought it up, FYI.

 

The geodetic coordinates of "Benchmarks" (section and plat monuments) used for property surveying in the U.S. (well, most everything West of the Ohio River anyway) have nothing to do with anything really, since property lines are defined in terms of those monuments without reference to geodetic coordinates. When using GPS for land surveying, Very good coordinates are established for them using known good USGS GPS points.

 

Back on topic. What everybody else said about maps in general being very inaccurate. However, the Satellite photo database available from terraserver.com appear to be very accurate. USAPhotoMaps is a favorite tool for viewing and using those photos.

[+badlands]

Magellan MapSend Direct Route on my Explorist 500 shows that I'm in the ravine about 300 yards from my house when I'm actually in the driveway. Once I get to the highway its dead on.

 

I drove to Atanata (about 500 miles), accurate all the way. On the way back I took a shortcut through the Smoky Mountains, much less accurate. It seams like the map makers have given urban areas and major highways more attention.

 

Overall they are incredibly good.

[+Team Cotati]

Mappoint by Microsoft is VERY accurate.........though not perfect. Not sure if perfection is their goal either. Afterall you must assume that they want a product that is affordable to people other than their Chairman and Chief Software Architect.

[+Alan2]

Their inaccuracies is one of the reasons for "Lock on Road" in your GPS That will generally keep the "car" icon moving on the correct road as you move around. Also, "Lock..." is there since the GPS's accuracy keeps shifting depending on obsturctions you pass such as mountains, foliage on the side of the road, buildings, etc. which also add to the incorrect position.

 

Also, on Mapsource at least, when you zoom down you get a message on the screen that says "Overzoom" the mfr's acknowledgemet you're getting into an inaccuracy area.

[+miles58]

MDAgent,

 

I use Lowrance mapcreate. At full magnification with a good reference like two roads I know to be accurate on the map in the computer I could easily place caches with the map software and a 100 foot tape measure. The accuracy of the placement can be as good as the best fix from my GPSr.

 

That *only* works if I know absolutely that the two references are dead on.

 

My mapping software also shows a town twenty miles off, businesses varying distances off (as much as several miles), and many roads in the wrong place.

 

I wouldn't do it as an experiment, much less as a means to an end, it's just not practical to survey first to see if I had a good reference.

[+wolf452]

removed, already covered.

Edited May 8, 2005 by wolf452