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thoughts on DEM and derived hill shade resolutions & map scale

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#1
Karsten Vennemann

Karsten Vennemann

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Hi All,

I am doing some "research" on Digital Elevation Model resolutions and derived hill shades for cartography purposes. For a future project a client will have me generate hill shades for the entire US in multiple resolutions. Source data for the hill shade will be 1 arc, 1/3 arc and 1/9 arc US NED datasets. We will want to use the generated hill shade raster as background layers for a web mapping application. In preparation for the actual work and in order to create a work plan I am doing some research into this. I would like to come up with two things:
a.) determine the map scales appropriate for which the 3 source data sets can suffice (scales at which the hill shade looks good and not pixilated)
b.) determine a map scale threshold that is to big (totally zoomed in ) at which the hill shade becomes useless for the user (and possibly detailed contours lines are still useful e.g. on "parcel" level or so)

Loading some hill shades in different resolutions (derived from DEM data between 3m and 90m) and using visual inspection at different resolutions I came with the following rough table of hill shade resolutions and applicable map scales (of course this reflects my personal, subjective take on this):

DEM source data of hill shade in m | Maximum zoom scale (zooming in more makes the map look pixely)

1 m -> 1:5000
3 m -> 1:15000
10 m -> 1:50000
30 m -> 1:150000
90 m -> 1:500000

I could not find anything on the internet related to this so do you have any input on this or thoughts on a.) and b.) ?
Does the table above that I came up with look reasonable to you ?

Thanks for any input
Cheers
Karsten Vennemann

Terra GIS LTD
Seattle, WA
USA
www.terragis.net

#2
Charles Syrett

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There was a recent thread in which a similar topic was discussed. I gathered together the notes I'd made over the years about DEM resolutions and posted them as an excel file. You'll see that I'm including more than just NED, but the recommendations for scale use are similar to yours. As you pointed out, this is not an exact science; much depends on how the relief will be displayed (colours, etc.) as well as where it fits in the visual hierarchy of the map. I would very much like to see the results of your research!

Charles Syrett
Map Graphics
http://www.mapgraphics.com




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