Elevation Vectors, Contour Vectors

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This topic contains 2 replies, has 2 voices, and was last updated by  Tom 7 years, 5 months ago.

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  • #3394

    electrify
    Participant

    Congratulations on a great resource, especially like the open source aspects of Natural Earth combined with quality data.

    My understanding is that Natural Earth has bathymetry vectors but no elevation/contour vectors, although data is available in raster form as cross blended hypsometric tints. A couple of questions in this regard:

    1) Will elevation/contour vectors be developed anytime soon?

    2) What is the thinking as to whether its worthwhile developing elevation vectors, i.e. what is the elevation vector back story?

    3) What open source software and workflow do you recommend for creating elevation contours with solid fill colour ramps (not cross blended or graduated)

    4) Sources of appropriate/ good looking colour ramps?

    5) Open source software and workflow for simplyfying elevation/contour polygons

    I have tried playing round with Aster Dems, QGIS and GDAL with limited success, my aim is to create some maps in svg format looking something like http://upload.wikimedia.org/wikipedia/commons/9/92/Isle_of_Man_topographic_map-en.svg

    #4053

    Nathaniel
    Keymaster

    That’s a nice map of the Isle of Man!

    1) No vector elevation data is planned at this time. For a map of Isle of Man, you would need more detailed data than we provide with Natural Earth, which is to 1:10,000,000 scale. There are many sources of 1km scale digital elevation models. But ur’re right, it is frustrating to step from a 90 meter dem back to desired scale, srtm or otherwise.

    2) I’ll ask Tom to fill in the back story on that. It is not a simple task.

    3) Any raster software can make abrupt transition elevationtints for u. Instead of spacing the breaks far apart, stack them close together (instead of 1000 and then 2000, do 1000 and 1001). I prefer using the cheap Natural Scene Designer for generating my shaded relief and color tints.

    4) Try looking at Tom’s website for tutorials.

    5) it is better to resample the source digital terrain model (dtm / dem) to near your target scale and resolution and then generate new contours. Generalizing contours to another scale is rarely successful.

    5) Open source software and workflow for simplyfying elevation/contour polygons

    #4054

    Tom
    Participant

    Electrify,

    Let me echo Nathaniel and say what a nice looking Isle of Man map you made.

    We have no immediate plans to add vector hypsometry to Natural Earth, although I looked into creating such a data set. I opted no to do it because of technical problems and a lack of time. River valleys are the main problem. When generalizing contours in narrow river valleys they tend to coalesce and over lap one another necessitating a huge amount of manual editing. Also, generalized contours in valleys also tend close at the narrowest sections creating false depressions upstream instead of linear contours that align to the river.

    Creating vector contours for Natural Earth would take about 400 hours to do correctly.

    However, other alternatives exist. The easiest and quickest way I know of to create elevation tints is by sticking with raster output. In “render shaded relief” palette of Natural Scene Designer you can specify elevation colors not to blend and turn the shading amount to 0 percent to create nice hypsometric tints. Rendering the tints at high-resolution will help result in sharp elevation breaks, although not as sharp as vector data.

    Eduard Imhofs “Cartographic Relief Presentation” by ESRI Press contains several classic color schemes for elevations. Otherwise, I’d just search the web and tinker with colors to create a ramp that I like.

    I hope that this helps.

    Tom

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