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post #16 of (permalink) Old 07-02-2009, 12:12 PM
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Oh baby

Quote:
quote:
New Toporama Web Map Service (WMS)
The Toporama WMS, a new Web Map Service provided by the Earth Sciences Sector (ESS) of Natural Resources Canada (NRCan) is now available on-line! This new service offers upgraded viewing characteristics and updated topographical data on a regular basis (6 months release). The WMS-Toporama Service is composed of different topographic data stores and is offered under 16 layers of information, grouped by type under different scales such as: CanVec files at the scale 1:50,000, National Topographical Data Base (NTDB) at the scale of 1:250,000 and Atlas of Canada topographic data at a scale of 1:1,000,000. This variety of scales offers many options for data representation to meet user's needs.
[]
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post #17 of (permalink) Old 07-06-2009, 11:13 AM
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http://ftp2.cits.rncan.gc.ca/pub/canmatrix/50k_300dpi/

There are some maps here that people can use, especially if they have access to a plotter.

I don't know how long these will be made available, so it might be prudent to download all the 1:50 000 topos that you like.
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post #18 of (permalink) Old 07-06-2009, 11:30 AM
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Quote:
quote:Originally posted by Eryne

http://ftp2.cits.rncan.gc.ca/pub/canmatrix/50k_300dpi/

There are some maps here that people can use, especially if they have access to a plotter.

I don't know how long these will be made available, so it might be prudent to download all the 1:50 000 topos that you like.
They've been there for a couple years already so hopefully they will stay! If you go up a directory you can get the 1:250k maps as well.

I find you can fit quite a reasonable area on a 8.5x11 sheet (just crop the portion of the map you need, 2300x3000 pixels is about the right aspect ratio and works out to 1:50k on 8.5x11").
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post #19 of (permalink) Old 07-06-2009, 12:11 PM
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Quote:
quote:Originally posted by Eryne

http://ftp2.cits.rncan.gc.ca/pub/canmatrix/50k_300dpi/

There are some maps here that people can use, especially if they have access to a plotter.

I don't know how long these will be made available, so it might be prudent to download all the 1:50 000 topos that you like.
These are great, but check out the link in juandefuca's post.
Quote:
quote:Originally posted by juandefuca

Another great resource is the GeoGratis website : http://geogratis.cgdi.gc.ca/frames.html
At that site, you can find a link to the geo-tiff's that you reference, but you can also get them in pdf format, which is much more convenient for some purposes. It doesn't look temporary.

choose 'English'
and then click on 'Download Directory' in the left hand menu. Then click on
'Raster Data'
and
'Scanned Maps'
and
'CanMatrix - Print Ready, Digital Topographic Maps of Canada'

I think the link you gave is available under

'CanMatrix - Georeferenced, Digital Topographic Maps of Canada'
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post #20 of (permalink) Old 07-09-2009, 11:03 PM
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Quote:
quote:Originally posted by ShadowChaser

... BC exists within multiple UTM zones - generally for a map to be "pannable" dynamically like Google maps you need to have a single map projection for the entire system - can't do that for all of BC accurately if you use UTM.

I believe they use BC Albers Standard Projection which is "Albers Equal Area Conic" rather than "Universal Transverse Mercator". I'm sure someone will correct me though, but AFAIK I think that's why most online maps don't show the UTM grids.
You are correct. BC spans five UTM zones. The BC Albers projection was developed to show the entire province in a single metre-based coordinate system.
I haven't checked out the latest interface for the BC basemap, but I remember having the ability to turn on a UTM grid, provided that I was zoomed into an appropriate scale where multiple UTM zone weren't evident.
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post #21 of (permalink) Old 07-10-2009, 12:39 PM
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One more thing; the online maps are not 1:20,000, they are are 1:50,000. The tool allows you to zoom into "1:20,000" scale, but this does not improve the level of detail and accuracy of 1:50,000 scale data, it only magnifies the error associated with 1:50,000 scale and presents it at 1:20,000 scale. The BC Basemap is 1:20,000 scale data and is far superior to the 1:50,000 in all respects. In fact, that was the whole reason for developing it.
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post #22 of (permalink) Old 07-10-2009, 12:49 PM
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Quote:
quote:Originally posted by magnetite

One more thing; the online maps are not 1:20,000, they are are 1:50,000. The tool allows you to zoom into "1:20,000" scale, but this does not improve the level of detail and accuracy of 1:50,000 scale data, it only magnifies the error associated with 1:50,000 scale and presents it at 1:20,000 scale. The BC Basemap is 1:20,000 scale data and is far superior to the 1:50,000 in all respects. In fact, that was the whole reason for developing it.
I don't even know what maps you are talking about here, but I find using the scale of the map to indicate the level of detail to be pretty strange. What difference does it make what scale you plot a map at? It doesn't change the level of detail. I can take a 1:50000 map and enlarge it 2x. That makes it 1:25000 but does not increase the detail of course.

If you're talking about contours, what matters is the spacing of the data points in the elevation data, the contour spacing, the algorithm used to determine the contours (either automatic or by a human I guess) etc.

Maybe there is some sort of standard used by the cartographic community that defines the required contour detail for various scales, but it seems like a dumb system.
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post #23 of (permalink) Old 07-10-2009, 02:16 PM
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You're correct - you don't know what you are talking about here. The 1:20K TRIM map is not just a 1:50K NTS map blown up to a larger scale. It is an entirely new survey with a different contour interval and a lot more detail. Try comparing the NTS 1:50K map of the Sky Pilot group to the 1:20K TRIM map of the same area and you'll quickly understand.
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post #24 of (permalink) Old 07-10-2009, 02:21 PM
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Quote:
quote:Originally posted by Dru

You're correct - you don't know what you are talking about here. The 1:20K TRIM map is not just a 1:50K NTS map blown up to a larger scale. It is an entirely new survey with a different contour interval and a lot more detail. Try comparing the NTS 1:50K map of the Sky Pilot group to the 1:20K TRIM map of the same area and you'll quickly understand.
???

I totally understand that, it's just that the size of the paper they print the map out on is not what gives it more detail, it's the "entirely new survey with with a different contour interval and a lot more detail" that does it.

If I take a 1:20k trim map and print it out twice as big it is 1:10k but no more detailed. So specifying the scale does not give you information on how detailed a map is. It just tells you what the scale is.
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post #25 of (permalink) Old 07-10-2009, 02:29 PM
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Well - that's not the way the online mapping works. For example if you use the iMap BC, at scales of over 1:80,000 it displays the 1:250K scale contours and mapping, and at scales of 1:79K or less it uses the 1:20K TRIM mapping contours. The reason being, you can't just display a 1:20K map at 1:200K scale and expect it to be usable - there will be so many contours it'll be totally black. You can't endlessly blow up or shrink down any map at all. You can even see this in the Google Map, as you drill down into it it access different databases and shows more detail at some zoomed scales that is pruned at higher scales.
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post #26 of (permalink) Old 07-10-2009, 02:47 PM
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Quote:
quote:Originally posted by Dru

Well - that's not the way the online mapping works. For example if you use the iMap BC, at scales of over 1:80,000 it displays the 1:250K scale contours and mapping, and at scales of 1:79K or less it uses the 1:20K TRIM mapping contours. The reason being, you can't just display a 1:20K map at 1:200K scale and expect it to be usable - there will be so many contours it'll be totally black. You can't endlessly blow up or shrink down any map at all. You can even see this in the Google Map, as you drill down into it it access different databases and shows more detail at some zoomed scales that is pruned at higher scales.
Right, so I guess it comes down to the idea I was trying to mention in my original post: that there is some "expected level of detail" for a given map scale, because at some point it becomes unusable. Of course this also applies to text labels that need to be legible etc. Unfortunately I don't think there's any standard "level of detail" vs "scale" correspondence. So it is possible to get different maps at the same scale from different sources that do not have the same detail level.
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post #27 of (permalink) Old 07-10-2009, 03:00 PM
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Apologies for the long winded explanation, particulalry if you already know this (its obvious you know far more than average).
Quote:
quote:Originally posted by swebster


I don't even know what maps you are talking about here
I was refering to the 1:50:000 scale maps referred to in the first post of this thread.

Quote:
quote:
I find using the scale of the map to indicate the level of detail to be pretty strange. What difference does it make what scale you plot a map at? It doesn't change the level of detail. I can take a 1:50000 map and enlarge it 2x. That makes it 1:25000 but does not increase the detail of course.
I agree completely. Though, "level of detail" is a pretty ambiguous term in the mapping industry, and one which I have never seen on a contract. Perhaps it refers to how much is shown on the map, as apposed to how accurate the map is (in terms of position). Mapping projects are designed with a level of error in mind, not a level of detail. Projects are designed to keep the amount of error, not to an absolute minimum, but within limits appropriate for the scale that the maps will be published. For example, a typical, and long running standard for the publication of maps in Canada, is that 90% of objects on the map should be within 1/2 mm of their "true" positions (relative to each other and the coordinate grid on the map), regardless of map scale. You can use the rule of thumb formula m=scale/2000 to calculate what the metre equivalent is for 1/2 mm for any map scale, and hence the error for any scale (or at least the error that 90% of the objects will have less than). For example 10,000/2000 = +/- 5m error for 1:10,000 scale maps. So, map scale is not an indicator of "level of detail" but it is a very strong indicator of the level of error present on the map, provided it was a well made map (this standard only applies to maps made for government publication or engineering purposes; it doesn't apply to commercial or trail-maps, for example).
If we're told to collect data appropriate for making 1:10,000 scale maps, we have enough experience to design a project that will collect data with less than +/- 5m error. Attempts to reduce the error further often lead to going over budget.
Contracts often specify what features are to be included or excluded from the mapping process; which I suppose naturally could be considred the "level of detail", though there is no standard in place to determeine what the "level of detail" is for a particular scale, like there is for level of error. Itwouldn't make sense.

Quote:
quote:
If you're talking about contours, what matters is the spacing of the data points in the elevation data, the contour spacing, the algorithm used to determine the contours (either automatic or by a human I guess) etc.
True, but the spacing of elevation data points is only part what matters when making contour lines. There are many other considerations. Only one of them being the vertical accuracy of those points.

Quote:
quote:
Maybe there is some sort of standard used by the cartographic community that defines the required contour detail for various scales, but it seems like a dumb system.
Again, "detail" is a fairly ambiguous term. The standard for producing contour lines is that, similar to above, 90% (sometimes 95% depending on the contract) of a contour line should be within +/- 1/2 the contour interval. For example, for 10m contour lines, 90% of any contour line should be accurate to within +/- 5 metres. If you have 20m contour lines, a point on the ground that lies along a 100m contour line can be anywhere between 90m and 110m actual elevation, and the contour line will still be considerd to be a good one within standard. Elevation mapping projects are also designed around an error value. If 2 metre contours are required, we have enough experience to collect data that will have less than +/- 1m error.

The interval we choose when making the lines primarly depends on the vertical accuracy and horizontal spacing of the elevation data we collected, but it also depends on the terrain within the map area. If its flat, a tighter contour interval works; if its steep, a larger interval may be more appropriate. As you have stated, this has little to do with map scale. Even if you had elevation data accurate to +/- 1m, you wouldn't publish a 1:20,000 scale map with 2m contours; unless the area was flat you would see nothing else but contour lines.

If you want to PM me for a discussion, feel free. I'm a project manager at an engineering/mapping/surveying company, and an occasional mapping/GIS instructor at BCIT.
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post #28 of (permalink) Old 07-10-2009, 03:05 PM
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Thanks Magnetite, that explanation is great.
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post #29 of (permalink) Old 07-14-2009, 09:46 PM
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I LOVE that site. I used to spend hours exploring certain areas. Now it's Google Earth. lol
An easier addy is just type atlas.gc.ca, select your language and click "view our topographic maps"
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