7 replies to this topic

[Bryan Krouse]

Hi all,
I am creating a project of my own where I am designing a wall map (4' X3') that has a grayscale shaded relief as a basemap for the contiguous 48. Is there any place I can download this data? I would like to use it in GIS and Illustrator to make the final map. Also, what scale is best for this size map?

Thanks,
Bryan

[Hans van der Maarel]

I am creating a project of my own where I am designing a wall map (4' X3') that has a grayscale shaded relief as a basemap for the contiguous 48. Is there any place I can download this data? I would like to use it in GIS and Illustrator to make the final map. Also, what scale is best for this size map?

There's a couple of ready-made datasets available for download:
Natural Earth
Shaded Relief Archive

Scaling is hard to determine, because it'll partly depend on the projection you pick. However, since you mention 4 x 3 feet your shaded relief has to be at least 14400 x 10800 pixels if you want to print at 300 dpi. You can probably get by with a bit less resolution, or slightly upsampling, you'll have to do some test prints to see how it works out.

[Charles Syrett]

If by "what scale should I use" you mean "what resolution DEM should I use" (Hans appears to assume that this is what you mean), then you may find my guide to DEM resolutions to be helpful. This is not meant to be authoritative or set in stone; it just reflects what I've found has worked for me over the years.

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

[AndyM]

... if you want to print at 300 dpi.

I've found that 150 ppi is ample for shaded relief on the reference maps I work on: printed, small-to-medium scale, where the relief is not the primary focus.

Shaded relief is pretty smooth, and as a background layer you probably don't want sharply-defined ridges anyway. To make these visibly sharp you would need high-contrast shading which would interfere with the legibility of overlying features and type.

150 ppi gives a pixel size of about .0067 inches square, with a diagonal size of .0095 inches.

I know this sounds coarse. I usually add lake colours (and other colours) to my shaded relief image, and of course on top of this I add lake shorelines (vectors) with a blue line about .006 inches wide. When viewing this in Illustrator or ArcMap I see corners of blue pixels on the land side of the vector shoreline (and corners of land-colour pixels on the water side).

But for a printed map this never shows up, even under a magnifying glass. The vectors appear as solid ink, but the background image ends up being halftone-screened anyway.

This is not a matter of being "good enough" -- when printed, you cannot see the difference between 150 and 300 ppi.

So if I'm confident that I know the output format I go with the smaller, more manageable file size.

Maps destined for PDF or other unscreened formats are a different story, although the need to zoom in to the scale needed to see the pixel-vector mismatch is questionable.

[Bryan Krouse]

I am creating a project of my own where I am designing a wall map (4' X3') that has a grayscale shaded relief as a basemap for the contiguous 48. Is there any place I can download this data? I would like to use it in GIS and Illustrator to make the final map. Also, what scale is best for this size map?

There's a couple of ready-made datasets available for download:
Natural Earth
Shaded Relief Archive

Scaling is hard to determine, because it'll partly depend on the projection you pick. However, since you mention 4 x 3 feet your shaded relief has to be at least 14400 x 10800 pixels if you want to print at 300 dpi. You can probably get by with a bit less resolution, or slightly upsampling, you'll have to do some test prints to see how it works out.

Hans,
I went with Natural Earth's (1:10m) raster. I clipped this to the contiguous US and enlarged it to 4 ' X3' in ArcGIS. I exported the raster as a TIF which is 9,600 X 7,200, which is smaller than what you described above. Is this going to produce a poor quality image?

[Hans van der Maarel]

I went with Natural Earth's (1:10m) raster. I clipped this to the contiguous US and enlarged it to 4 ' X3' in ArcGIS. I exported the raster as a TIF which is 9,600 X 7,200, which is smaller than what you described above. Is this going to produce a poor quality image?

Maybe not. It depends on a number of things:

• The distance from which the map will be viewed. There's a certain minimum angular size the average human eye can distinguish and that can be calculated to certain sizes at certain distances. I'll see if I can figure it out again.
• Whether or not there's any other information on the map that's visually more important than the hillshade. Based on what Charles and Andy have explained, I'd say you're probably going to be okay with the resolution you have at the moment.
• The output medium and printing process.
• Your definition of "poor quality"

I suggest you do a test print and decide based on that.

Incidentally, there's a 500m Natural Earth dataset for the Lower 48 available too: http://shadedrelief....s/download.html (scroll down a bit)

[Bryan Krouse]

I went with Natural Earth's (1:10m) raster. I clipped this to the contiguous US and enlarged it to 4 ' X3' in ArcGIS. I exported the raster as a TIF which is 9,600 X 7,200, which is smaller than what you described above. Is this going to produce a poor quality image?

Maybe not. It depends on a number of things:

• The distance from which the map will be viewed. There's a certain minimum angular size the average human eye can distinguish and that can be calculated to certain sizes at certain distances. I'll see if I can figure it out again.
• Whether or not there's any other information on the map that's visually more important than the hillshade. Based on what Charles and Andy have explained, I'd say you're probably going to be okay with the resolution you have at the moment.
• The output medium and printing process.
• Your definition of "poor quality"

I suggest you do a test print and decide based on that.

Incidentally, there's a 500m Natural Earth dataset for the Lower 48 available too: http://shadedrelief....s/download.html (scroll down a bit)

Hans,
I really appreciate you taking the time to field my questions. The shaded relief is not of huge importance...it's more of a 'basemap'. Placed on top of the relief will be the state boundaries, office locations, and production sites, which are the important variables. I am downloading the 500m and will see how this compares. I will certainly do some test prints.

I am doing this project because I am poor at raster data and am interested in improving my skills.
Thanks for your input.
Bryan

[SaultDon]

There is also an interesting article I was reading from an ArcGIS blog: Mapping Center

On mapping scale and raster resolution

Excerpt:
In 1987, Waldo Tobler, renowned analytical cartographer (now emeritus from University of California-Santa Barbara) wrote, "The rule is: divide the denominator of the map scale by 1,000 to get the detectable size in meters. The resolution is one half of this amount." Tobler goes on to note, "Of course the cartographer fudges. He makes things which are too small to detect much larger on the map because of their importance. But this cannot be done for everything so that most features less than resolution size get left off the map. This is why the spatial resolution is so critical."