The topological "standard" is definitely to create a single map layer of all geologic polygons. Each polygons carries a number of attributes (which of course can be used to split out subsets, either as permanent layers if that what a user wants, or as queries.) Furthermore, there should be a single layer of geologic polylines which include all contacts and faults, again each with appropriate attributes. The geologic polygons should be build from this topologically clean set of lines, which are digitized.
The only exceptions to this topology are those which actually make geologic sense too: geologic polygons which "cross or overly" rock types (e.g. alteration, laterite) should go in their own layer. Building the topology of geologic maps is actually very close to fieldmapping itself, distinguishing rock type from alteration, having one line on a map in one place etc. etc. Lastly, there will be different scale maps depending on the project etc. A regional map (e.g. 1:50,000 or even 1:5,000,000) will contain different rock (map) units than a detailed map (1:200 or 1:5000 even.) Sometimes the more regional scale maps will be a "lumping" of the more detailed map units identically, but usually it doesn't work out this way. There should be different maps for each scale and which is used, depending on the need. The more regional polygons should not be split against the detailed ones but one might make the regional map out of the more detailed polygons by coloring on different attributes (e.g. all felsic intrusives are colored tan (the geologic term is lumping) in a regional VIEW of the map, but colored a range of colors depending on specific composition and age Ithe geologic term is splitting) for the more detailed VIEW. Cinda Graubard GeoMax At 10:55 PM 06/27/2005, [EMAIL PROTECTED] wrote: >There appear to be two end members on how to create geologic map polygons. >One is to create a single layer that contains separate polygons for every >formation/ outcrop/ zone (no matter the size). The other is to create a >series >of layers that contain polygons of various sizes. One layer would contain >broad/large scale polygons while other layers would contain detailed polygons >that >would appear to be within the larger polygon [but not digitized as an island >or lake]. I have seen both styles used. > >Is one method technically better than the other or is the method choice >dependent on what the end use will be? what do the members of this list >prefer? > >sandy figuers >norfleet consultants --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 16969
