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new to GPS with some questions

Started by ilbob, December 02, 2011, 06:07:30 PM

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ilbob

My wife bought me a GPS for xmas last year. Its a garmin etrex vista H.

I have been using it on my hiking excursions since I got it but mostly just to track where I have been. You can see some of the treks on my blog, but it won't let me post a link here for some reason.

I am too cheap to buy maps so I looked for free ones and came upon this place.

A few things I have run into.

There seem to be a fair number of mistakes and or omissions in the IL topo map I downloaded. Missing water features, roads and water features shown that don't actually exist. Is this common? Am I being too picky about something that I got for free? I have noted some of the same mistakes in google maps so I am wondering if the base data that both came from are the problem.

Is there a good tutorial somewhere on using the various features. I have been able to figure out the compass. It took me a while to figure out it was off by default and had to be turned on to use. In reality it did mention this in the manual but I sort of went past that part pretty quick.

I was able to use it on one hike to convince myself I was in WI when I was not real clear just where I was.

I have been able to add waypoints on the trail but, have not figured out quite how to use them for much of anything.

One other thing I have noticed. The GPS trip computer often shows a shorter distance walked than the time involved and base camp says. Sometimes it is pretty close but other times there is a substantial difference. I have come to the conclusion that the distance basecamp calculates is closer to the truth than the trip computer. It seems odd given they start at the same point and end at the same point.




maps4gps

Unfortunately, there is no one source of publically available data to use to build these maps; and the various data sets we conbine to make a 'topo' map were each designed for other purposes.

The hydro is from USGS digital files of their printed 1:24,000 topo maps and they are now constantly altering it for 'updates' - some of which make it 'unusable' in an area for awhile.
Are you comparing the mapset's hydro to a 24K topo or actual ground conditions?

Transportation data is from Census TIGER files.  The locations have gotten better in the past few years, but the attribute coding can be very incorrect - Census created them to aid Census field personal.  USGS has recently change the National Map from Census TIGER transportation to commercial vendor.  Some State DOTs have files available - these can range from very good to very old and/or usless.


ilbob

I noted the inconsistencies recently while hiking in a forest preserve and DNR area.

The water features shown on the GPS map are not even close to what was actually there on the ground (some of which can be plainly seen from Google satellite images). The maps also showed roads that just plain did not exist.

maps4gps

Garmin's website allows you to view an area of your choice for some of their map products.
What does their 24K mapset show for this area? 

Boyd

#4
Those sound like common errors you will find with many maps available here, unless the author has hand-edited the data or found alternate sources than the ones commonly used. The NHD data is only good up to a point. I have a stream running through my own property, and the NHD doesn't even come close to putting it in the right place or showing each little bend. But neither does a "real" USGS 24k topo.

I am just now finishing a major update to my map of New Jersey, and I have spent extensive time hand-editing the road data based on aerial imagery and personal knowledge. Have also used NJDOT maps to reclassify and number county routes, something completely missing from TIGER as well as Garmin maps (although, interestingly, you can see these route numbers if you go to Navteq's site).

My state also has very high resolution (12k) landcover vector data which I am using. This data includes a lot of wetlands, small lakes and vernal ponds that are completely missing from the NHD data or Garmin's maps.

Bottom line is that it's a lot of work to make very accurate and detailed maps. My personal focus has been to continue refining the details of my local area over a period of years.  Others have focused on providing maps for lots of different places using the common data sources. Both are worthy endeavors IMO, and it's great to see so many free maps here that cover so much of the US.

When you start getting particular about the map details and want something better (as I did), then it's time to learn how to make you own maps and give back to the community by sharing them. :)

ilbob

Quote from: maps4gps on December 03, 2011, 08:49:47 AM
Garmin's website allows you to view an area of your choice for some of their map products.
What does their 24K mapset show for this area?

I poked around their website and never found anywhere to look at a map. Buy yes, look no.



babj615

@ilbob, can you give us a Lat/Lon of an example water feature?

While I understand my experience will not necessarily be your experience, I found the maps available here for my corner of the world to be several orders of magnitude better than Garmin's most recent 24K Topo's.

By better, I mean more detail, more information, and more accurate information...

I consider myself very fortunate to have access to such wonderful maps, and use them exclusively on my GPSr's.

Having said that, there are a few errors I have discovered, mostly streets that do not exist, which are present in every map source I have checked them against, including Google and Bing, which leads me to believe they are present in the source data which is provided by our government agencies. What do you expect from them? Certainly not perfection!

Regarding water features, I do not know what area you are in, but I would imagine they can change course and location slightly over time, especially after some of the abnormal weather some areas of the US have seen in recent months and years. I do not know that it is feasible to have people monitoring every little stream for every little change after every winter storm....

Map making, it seems, is an imperfect science, and I am truly blessed to have access to the maps I do here at GPSFileDepot.

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ilbob

Quote from: babj615 on December 03, 2011, 11:03:24 AM
@ilbob, can you give us a Lat/Lon of an example water feature?
I have a really good example shown on my blog but I can't post links for some reason. Maybe did not pay dues or something?

BTW, the latest IL map is nicer than the previous version I was using. Thanks to whoever it was that spent the time and effort to make it.

This is where I first noticed it. N42 29.889 W89 15.546

There is a good sized horseshoe pond that straddles the IL/WI state line here. It has been there for a long time. It can be easily seen from google earth or google satellite images. but is not on any map that I have been able to find except the forest preserve district's map of this forest preserve. heck the maps don't all even show the FP, and the ones that do have the boundaries wrong.

On the new IL map I just downloaded from here, at Rock Cut State Park NE of Rockford, IL an entire lake (Olsen Lake) is just missing on the east side of I39. It is a good sized lake that has been there quite a while. Oddly, it also now shows Willow Creek coming out of the west end of Pierce Lake as an "intermittant" stream as it exits the park to the west. There is nothing intermittant about that creek. On the bright side, it now shows Perryville Road (the western boundry of the park) where it really is instead of showing it 100 yards inside the western edge of the park like the previous version did. Many of the internal roads in the park are also now shown. They are not all there, but more of them are then in the previous edition.

jbensman

There is lots of problems with the hydrolgy in IL.  Do you have CityNavigator?  My Topo (coves all of IL) is a tranparent overaly map designed to work with City Navigator.  I have traced thousands of lakes, wetlands, etc in GoogleEarth to add to the maps.  I have also removed numerous items that are no longer there.  CityNavigator many times shows water features whee they don't exist in numerous places.  My Topos will cover up many of these places that inccorectly show in CN as water and make them show as land.  People can tace missing stuff in GE and send it to me and I will add to My Topos.  Errors can be corected too.  Many times you can see the corect location of a stream in GE or trace the surface of a stream.

CityNavigator tends to have errors on roads.  Many parks tend to have lots of missing roads or roads that are no longe there.  My Trails will add missing roads and it will also cover up roads that are not there.  I make lots of the corrections but anyone can send me oads that need to be covered in CN or are missing.

Eastern Land Ownership has lots of public lands identified.  And people can send corrections or additions.

All of these maps cove all of IL (so does My POIs) and are transparnt and show ontop of other maps like City Navigator.