Jump to content

 
Photo

Simplifying coastlines and state boundaries

- - - - -

  • Please log in to reply
3 replies to this topic

#1
Dennis McClendon

Dennis McClendon

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,083 posts
  • Gender:Male
  • Location:Chicago
  • Interests:map design, large-scale maps of cities
  • United States

You folks who regularly work from GIS files, how do you simplify the state boundaries and coastlines elegantly enough for small-scale (1:50M) publication? Do you just trace over them in Illustrator? Or are there some nice ones in shapefile format floating around somewhere?
Dennis McClendon, Chicago CartoGraphics
chicagocarto.com

#2
frax

frax

    Hall of Fame

  • Associate Admin
  • PipPipPipPipPipPipPip
  • 2,309 posts
  • Gender:Male
  • Location:Stockholm, Sweden
  • Interests:music, hiking, friends, nature, photography, traveling. and maps!
  • Sweden

tracing would likely give the best results, but can be time consuming.

I often generalize data in GIS, and then do a slight "Simplify" in Illy to save time (in most cases this is good enough)
Hugo Ahlenius
Nordpil - custom maps and GIS
http://nordpil.com/
Twitter

#3
CHART

CHART

    Chart

  • Validated Member
  • PipPipPipPipPip
  • 358 posts
  • No Country Selected

This site is a coastline extractor. Maybe the scales provided are not suitable. But I thought it worth a mention.

http://rimmer.ngdc.noaa.gov/coast/

As for generalizing, yes I would do it in a GIS environment (removal of small coastal islands, line generalization etc.) and would overlay both, non-generalized and generalized data to check to make sure my content is acceptable. Would also use a very high percentage of simplification in Illy (98-99%) just to do a final smoothing.
If you have to generalized two data sets for the same scale (adm. boundaries and coastline) you should make sure they overlay correctly when done. e.g. a shoreline used as a boundary will not necessarily match after generalization if they were in two different set to start off with. Lots of work around for this, but you get the picture.

Tracing over as mentioned will give you the subjective touch... but time might not be not on your side for this.

If you look around in various map data warehouses on the web you probably should find a good data set for 1:50m rep. already generalized...
Chart

#4
MapMedia

MapMedia

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,029 posts
  • Gender:Male
  • Location:Davis, California
  • United States

ArcMap has a generalization tool that can use either point-removal or bend-simplify while resolving topological errors (important! no gaps between polygons - as is created by using Illy simplify path). I prefer the bend-simplify option where you set the reference bend baseline (in any unit, e.g., miles).

The problem with the ArcMap tool is that to create a small scale map, I need the states, open water rivers/reservoirs along state lines, coastline polyline, state boundary polyline to MATCH 100%. Because the datasets are composed of nodes/paths at different locations and distances, the ArcMap generalization algorithm produces results that do not match up.

Alternatively, if Illy could simplify while snapping points (keeping polygons together without gaps), this would be great.

My current thought on this is to use ArcMap bend-simplify to create a small scale political boundary basemap then simplify and hand fix the hydrology in Illy.
There is a method to extract state boundaries and coastlines from generalized states - I am working on this now - and hope to get good results.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->