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CacheFreakTim

Difference between the 24k and 100k maps?

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On Garmins site it lists two different Topo map sets you can buy. The 24K and 100K. Maybe this is a really stupid question but what is the difference between the two? Also can you buy the entire US or do you have to purchase each region separately?

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The 24k comes in smaller sets because it has much more detail. It has routable streets and trails, but the latter does not do a lot of good because it has far less coverage of trails and fireroads than the standard garmin topo. Its detail has helped me find the right side of ridges in areas where neither maps show trails, but think about what you will be needing and whether it is compatible with your gpsr.

 

The 24k street navigation has worked fine on my Colorado, so if you don't have city navigator, that could be a plus.

Edited by Erickson

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Garmins ... Topo map sets ... 24K and 100K ...difference between the two?

The 1:24,000 are like the 1:24,000 printed USGS topo maps - although I have heard little, if any, of the trail information is in the Garmin product. The 1:100,000 product is more generalized, like the printed 1:100,000 maps and uses metric contour elevations converted to their foot equivalents. The 100K product has been around for a few years, while the 24K started being released this winter and only covers part of the country so far. The prerecorded micro cards allow them to be used in more than one GPSr, but not with MapSource and would require changing cards if the adjacent State is not on the same card. The DVD/CD version may be locked to one GPSr (100K is not locked, posts on 24K say yes and no), can be used in MapSource to select a smaller area of interest and add other mapsets (Garmin, 3rd party, your own). I do not remember about autorouting.

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I just purchased the North Central 24K DVD and loaded Montana maps onto my Oregon 300. I was really surprised with the inclusivemess of forest roads (dirt roads). It's a giant leap in road detail even over the custom maps available for free. Garmin seems to have scoured the internet looking for government published off-road and trail data, verified it, and included them in this excellent mapset.

 

For instance; there is a Helena city trails shapefile available online from the local government website. It is the only place that dataset is available and Garmin included it in the 24K mapset. I'm really amazed.

 

Detail may vary by state however and since Montana was so poorly covered in Topo2008 the 24K was a huge jump in detail. It was nice to navigate the forest roads via autoroute.

 

Earlier topo mapsets from Garmin left alot to be desired. In my opinion they hit a homerun with this new 24K product. Forget the 400T/550T versions of Oregon/Colorado handhelds. Get the units without paying extra for Topo2008 and get this mapset for your area instead. Not only do you get maps that you can peruse on your PC, you'll also get alot more data with much better accuracy.

Edited by yogazoo

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To simplify - think of a digital photograph. Higher megapixels = more detail. With topos, the opposite applies. Smaller designations = more detail for the topographic map details. 24K is better than 100K as others have said.

 

As a result those maps take up more space in storage and usually have more tiles (segments) which can put you up against device limitations for memory addressing.

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The 24K scale has been defined so as one inch on the map represents 2000 feet on the ground.

Now how many miles is it ? :o

 

In fact it is typical of the tricky stuff you got to do to accommodate an archaic and illogical measurement system.

 

A maps scale is just the ratio of the real world measure to its representation on the paper.

 

With a scale of 1/100000 for ex. , 1 cm on the map represents 1000 meter, that is 1km (any 10 year old kid and above knows that).

 

Topo map normally use 1/25000 scale, 1cm represents 250 m.

 

That means that on the same sheet of paper, you can print more details than with a 1/100000 scale but you cover less ground.

 

With US topo paper map, I found it easier to use the same logic but as the scale is 1/24000, 1 cm represents 240m, beats to play with a strange inch rule with fractions isn't ?

 

Now on a GPS screen, scale really doesn't mean much and the real meaning is that the 1/25000 scale has more details in it.

 

Now if you want to have some fun, look at the scales used in the US building industry !

Edited by Suscrofa

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To simplify - think of a digital photograph. Higher megapixels = more detail. With topos, the opposite applies. Smaller designations = more detail for the topographic map details. 24K is better than 100K as others have said.

 

As a result those maps take up more space in storage and usually have more tiles (segments) which can put you up against device limitations for memory addressing.

 

In areas of high relief (say rock spires) the 100k contours look sandblasted and some detail that shows on 24k may be totally erased on 100k. Check out Spider Rock in Canyon De Chelly. On most 100k maps it's just a misplaced POI.

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If you have a GPS with terrain shading the 100K topos only have an infused 30 meter DEM whereas the 24K series has a 10 meter DEM. The difference in the detail on the terrain shading is very noticeable. Relating to this, the Montana, and I would assume soon to be other models, utilize the Digital Elevation Model (thing used for terrain shading) to calculate some values relating to elevation such as the Vertical Distance to Destination field. In my experience the 10 meter Digital Elevation Model is very accurate (as is the 30 meter but with a bit less detail.)

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Now on a GPS screen, scale really doesn't mean much and the real meaning is that the 1/25000 scale has more details in it.

 

 

I would disagree. 24K maps are also more accurate on locations. A 100K paper map is not that detailed and drawn at a 100K scale. So the fact that the locations are not real accurate does not make any difference on a peper map. Unlike a paper map, you can zoom in on a 100K map on your GPS. Thus, on you GPS you can see the inaccuarcies of the 100K map. While on a paper map, the inaccuracies do not make a difference, but they make a difference on the GPS because you are using the map on a scale it was not intended to be used on. 24K maps are created on a different and more accure scale so they are more accurate on locations and when you zoom in, they are 4 times as accurate.

 

Here is another way to look at it. When you zoom in and out on your GPS, features are drawn at different resolutions and some things only show when you zoom in. Different zoom levels have grids with different spacing. Lets say you have a 10 mile section of a road. At zoom level 10 it would be drawn with 4 points and at zoom level 0 it would be drawn with 16 points. Using a 24K map would be like seeing the road drawn at level 0 with 16 points. Using a 100K map is like using the level 10 map with its 4 points when you zoom in.

 

Contour interval and the DEM resolution determines how accurate the contour lines are. I beleive the contour lines in Garmin 100K and 24K maps are the same as the USGS Maps. The maps you get from places like gpsfiledepot are normally more accurate than the USGS data. You can download elevation data (DEM) of various quality and resolution from USGS servers. We will normally use higher resolution DEM than the USGS maps so the free maps will generaly be more accurate than the USGS/Garmin maps. But its not that simple. For example, the DEM data I have used to create topo lines has 9 times the resolution of the USGS maps, but if I use the same contour interval, there is not that much difference in where the contour lines are. If I use a contour interval twice that of the USGS maps, it would still not be 9 times as accurate-it would only be about twice as accurate.

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If you have a GPS with terrain shading the 100K topos only have an infused 30 meter DEM whereas the 24K series has a 10 meter DEM. The difference in the detail on the terrain shading is very noticeable. Relating to this, the Montana, and I would assume soon to be other models, utilize the Digital Elevation Model (thing used for terrain shading) to calculate some values relating to elevation such as the Vertical Distance to Destination field. In my experience the 10 meter Digital Elevation Model is very accurate (as is the 30 meter but with a bit less detail.)

 

Are you sure that is the resolution of the DEM data? I was not aware anyone had figured out what resolution Garmin was using.

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