Geological base maps
Jul. 5th, 2010 @ 06:30 pm
needs to create a geological survey of a few square kilometres of the Lake District this summer. She wants to record observations in the field on paper then transcribe them to a computer somewhere less generally rugged.
To this end, she wants a series of sheets of A4 card, each printed with a National Grid kilometre square of base map. For convenience, this would be at either 1:10,000 (10cm×10cm) or 1:5,000 (20cm×20cm) scale.
She has access to the Edina Digimap OS collection, but their OS Explorer map (1:25,000) squares exploded by a factor of 2½ are pretty pixelated — and give the impression of being a re-scan from paper sheets in any case.
I've just taken a look at OS OpenData and downloaded the "OS Street View", "OS VectorMap District (Raster)" and "OS VectorMap District (Vector)" data for a specimen square: the VectorMap raster is cleaner and more detailed than Edina, but lacks paths, fences and — most crucially — contours; the StreetView is still cleaner and more detailed, and does at least have private tracks, but lacks spot heights as well as contours. So far as I can tell without a program that understands it properly, the VectorMap vector data is similar to the raster.
Do any of you know some more effective way to drive either Edina or OS OpenData? Alternatively, is there some other source of mapping data that would be more appropriate?
Edina Digimap also has geological maps, see here:http://edina.ac.uk/maps/
Digimap collections list: "Geology Digimap: geological maps and data from the BGS". Would that be better than the OS maps if this is a geological survey?
Otherwise I can suggest http://www.openstreetmap.org
for free data.
Also, OS vector maps should be scale-independent, i.e. if you zoom in, you should always get a clear picture, as the objects on the maps come in forms of mathematical points, lines and areas that are always exactly redrawn, regardless of the zoom. So it is not similar to raster (where you can zoom in only so much until all you can see are individual pixels).
Geological maps won't be of much use if I'm supposed to be creating my own - they'll already be filled in :) They're also unlikely to be at a suitable scale for the kind of thing I'm supposed to be doing for this subject. (In fact my institution doesn't subscribe to the geological maps collection - presumably on the basis that we've already got them all on paper - so it's a moot point.)
The OS maps that Digimap provides are unfortunately either raster or too schematic to be much use to me (it's very helpful to have crags, screes etc drawn on accurately; that, and the vector data available from Digimap lacks contours).
For contours and since you know ArcGIS - this is a long shot, but still, maybe better than nothing: you could go get the free DEM (digital elevation model) created from Shuttle Radar Topography Mission (google SRTM DEM to find it, it is available for the entire world), import that into ArcMap and create contours yourself.
|Date:||July 6th, 2010 01:34 pm (UTC)|| |
The resolution for SRTM would be too coarse for such a large scale map to be all that useful.
|Date:||July 6th, 2010 01:34 am (UTC)|| |
Having done this sort of stuff, I'd really recommend a GPS unit for the field work, if you have access to one. It makes data collection much easier, and it skips the step of digitizing the collected data.
However, quickly looking over Ordnance Survey, I think you're out of luck. OS street view only comes in raster for free, so what you get is it, although I admit it is exceedingly strange the maps don't have contours on them. Also, the free vector data is both a smaller scale (less detail, if still scale independent), and you need GIS software to read the shapefile format to make the map from scratch. However, with the vector data you probably could make a workable field map out of the district level
maps, and there is free GIS software out there, like GRASS GIS
, but unless you know your way around GIS software, it won't be easy.
It is really unfortunate that such a small and historically well mapped country has so little free data. My GIS teacher, who is originally from the UK, used to bitch about this, especially in light of the fact that the federal and provincial governments in Canada provide geographic data for free, as do the Americans.
|Date:||July 6th, 2010 09:52 am (UTC)|| |
Thanks for the recommendation of GPS. In fact my department frowns on it slightly so I probably won't end up using one, but I appreciate the suggestion.
I have access to - and a modicum of familiarity with - ARC GIS. I can see it won't be easy, though, so I'd slightly rather avoid that route!
I'm currently leaning towards going and buying topographic maps from the local OS centre, and trying to get the department's librarian to buy them off me after the fact.
Argh, surprise being-logged-out-of-LJ!
|Date:||July 6th, 2010 01:57 pm (UTC)|| |
How familiar with ArcGIS? Because you can make a decent basemap in a couple of hours with that data if you have enough familiarity. Otherwise, buying a topo map seems your best option.
(Sorry for the absence!)
Not very at all, yet; not enough to want to rely on it.
Thanks for the confirmation that buying the topo map is probably the best option!
|Date:||July 6th, 2010 10:32 am (UTC)|| |
Geological base maps from Digimap
Any raster dataset will have limitations on it's scale. The larger the scale, and the further from it's source resolution, the more pixellated it will get. This applies to all raster datasets. With the OS 1:25 000 raster data, it should display ok at 1:10 000. The source resolution specified by OS at the time of creation is 2.5m per pixel. This may well be a lower resolution than the newer VectorMap District or Street View datasets. Without trying this myself, it sounds as though a 1km square filling A4 paper is going to be sufficiently far beyond the source resolution of the raster datasets that a pixellated images is inevitable.
Have you downloaded the original TIF images from Digimap's Data Download service, or are you generating map images on the screen and taking screen captures of them from Roam or Carto? This will make a big difference.
If the raster datasets do not give you a good enough output, the next option is to download the Land-Form PROFILE data from Digimap (to create the contour layer) and overlay this on an alternative dataset, such as OS MasterMap's topographic layer or the OS 1:10 000 Scale Raster (both also available from Digimap). You will need access to GIS software to do this. While it is more effort, it will give you a map at whatever scale you choose without the pixellation effect of raster datasets displayed at non-source resolutions.
We are happy to continue correspondence on this with more detail if you would like to contact the EDINA helpdesk on firstname.lastname@example.org or telephone us on 0131 650 3302.
EDINA Geoservices Support
Many thanks for the reply. kaberett
can respond in detail this afternoon about what she needs, and about what she has or hasn't tried using Digimap (she has access to it; I don't).
However, she did give me one PDF that Digimap had produced and that's about 100 dots per inch for a 1:10,000 enlargement from an Explorer map. By my maths that is, indeed, 2.5m per pixel.
For reference, OS VectorMap District is 2.5m per pixel (50 dots per inch) and Street View is 1m per pixel (125dpi) — at least in the form they offered when I downloaded it.
However, the printed OS maps seem to be considerably higher resolution. At a guess, Explorer maps are printed at something like 1200dpi. That would equate to 0.5m per pixel, which would do the trick: 500dpi if enlarged to 1:10,000 and 250dpi if enlarged to 1:5,000. Unfortunately, it seems the Explorer maps aren't available in digital form at that kind of resolution (whether raster or vector).
|Date:||July 14th, 2010 11:17 pm (UTC)|| |
Re: Geological base maps from Digimap
Apologies for how late this reply is.
I was using Roam/Carto - I'd not gone far enough into the FAQs, clearly. Mea culpa.
Thanks hugely for taking the time to respond and for the suggestions as to the next steps to try.