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Topo map scales

Started by Forrest hunters, February 07, 2011, 08:33:53 AM

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Forrest hunters

Can anyone tell me about the Michigan topo map that is 24k scale and the Northeast Topo United States Part 1 of 3 Map?  I think that maybe the NE Topo is 100K scale?  Can anyone confirm for me as I have both loaded onto my Oregon and may want to remove one of them.


Scale in a digital product is not really definable like it is on a paper map.

What we refer to scale is related to the scale of the source date.

The data we use to build mapsets comes from various sources.  A data source itself may use data with more than one scale and sometimes does not even specify were the data comes from, etc.

There is also the question of how the 'scale' of digital source data compares with the scale of printed source data.

There are other concerns with the data source and sometimes the source data which is more 'detaild' is not overall the best to use.

That map author used the USGS NED (grided elevation data) with a 90 meter spacing.  Everyone else was using the NED dataset with 30 meter spacing.  Hence he used 1/9 of the points to build his contours which possibly looks more like 100k contours than 24k.  He also used a 20 foot contour interval for all 48 States; about 50% of the printed USGS 24k quads use a more detailed contour interval.

Anything specific which gives you this impression?
Use whichever one you feel is best for you needs.

Forrest hunters

Thanks for the quick reply. 

Anything specific which gives you this impression?
BY my house i see 3 times as many contour lines in the Michigan Topo vs. the NE Topo maps.  Thats why I asked.  Love the feedback you have given me.  Its been a long time since I have my serveying class in college and i guess i dont remember as much as i thought i did.

Also the reason i asked was I have both on my Oregon 450 and I may dump one of them as I am getting in a lot of cases 3 duplicate POI in that folder and my start up time is around 45 seconds to a minute and think it may be because I have duplicate data there.

I think i would like to have just a road map loaded on my gps and then a topo overlay so i can view just roads if i want.  Is there a way to get ride of the duplicate POI if i do that?



You could use my Planimetric - North Central and/or North East along with my Michigan contours20ft overlay mapsets.  In the contour overlay mapset I used a contour interval of 20 feet for the entire State to be consistent; thus it may only have half the number in the MI topo.
Two of the duplicate POI's may be coming from the MI topo as I included hydro POI's from both the USGS GNIS and NHD databases. 

Forrest hunters

I am torn on which maps i want.  i like the 10 foot contour map but sometimes i think it makes it a touch cobbled.  Other times i think it is perfect and i am sure there is never a happy medium.  I think that having the duplicates may be slowing the unit down some though.  What do you think?  If so I may dump the others for MI and just use your Mi topos which are awesome.


What do you mean by, "getting in a lot of cases 3 duplicate POI in that folder"  particularly "folder"?

What I don't like is when you use where to, geographic points, it will look from the maps I made (MY POIs and My Trails) and the built in 100K topos even though I have it disabled.  So I get multiple POIs for the same thing.  I wish it would only search ACTIVE maps!

You are not dispalying both topos at the same time are you?  Only enable one of them at a time.

I've got all kinds of maps loaded on my 550T (which works just like you 450) and I have never noticed it slowing the GPS down.  However, sometimes there is a slight delay when panning when there is lots of stuff on the screen like a high concentration of topo lines. 

Forrest hunters

jbensman, you are correct in my where to folder.  I do only have one map active at a time unless it is an overlayment map. 

My only slow down is when i turn it on it take 45 seconds to a minute to get to the home page.



With just about every Garmin unit I've owned (LOTS of them  ;) ) I've noticed an additional delay when you add maps. I think the unit builds some kind of index when it starts up maybe? I have a 16GB card that is completely full of BirdsEye imagery. When I insert that into my Oregon 400t, startup takes FOREVER - several minutes. Of course, that's probably something different than vector based maps...

Forrest hunters

I did a little test and without card in it is 12 seconds and 47 seconds with 4gb card with about 1.4gb worth of maps loaded on it. Does that seem too long?


No.  You cannot wait another 30 seconds????????

Forrest hunters

I can wait that long.  It just seems others are getting their units to start up a lot quicker than that with a lot more loaded on the cards.

I will see what speed my card is and maybe get a quicker card.


Somewhere in one of Garmin's FAQ items I recall they said that the larger the SD memory card, the slower the startup time. Not sure why this would be unless maybe it does some kind of sector scan at startup? They implied that the card size itself was an issue, and not the number of maps it contained.

Forrest hunters


Thanks for the input.  Are you on every forum for gps there is?  I see your screen name everywhere. 

I checked at lunch and my card is a 4gb and class 4.  I wonder if different manufacturers are different speeds?


Forrest hunters

Last night I did some testing with loading the maps. Below is a spreadsheet of what I did and the boot times there after. I did shut it down and turn it on 3-4 times after loading each map to make sure everything was good before i took these times. Does this sound like about what everyone else is getting. Do you think if I broke some of these larger files into a few smaller ones but still have all that info on there that it would speed things up? Maybe me being a newbe I am loading to big of files on there at once.

                                        start up time          file size
no card                             12 seconds
michigan topos                  14 seconds           146,536 kb
other michigan topo           14 seconds             59,299 kb
US states and counties       14 seconds              1,918 kb
US P North Central             25 seconds           335,832 kb
US P North East                 32 seconds            282,872 kb
NE Topo Part 1                  46 seconds            642,656 kb
Total 1,469,113 kb

Disk reads 1.40gb used 1,504,444,416 bytes

2.28gb free 2,452,291,584 bytes

3.68 gb capacity 3,956,801,536 bytes

Thanks again.


My *guess* would be that it's related to the number of map sectors and not file size. The one test that you didn't do would be to have a blank formatted card in the slot. I guess it couldn't make much difference though, because the small map file only resulted in 2 additional seconds of startup.

Nice science project there - thanks for posting your results!