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Pocket GPS World :: View topic - What is the best resolution for a scanned map?
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What is the best resolution for a scanned map?

 
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TC
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Joined: Oct 22, 2003
Posts: 119
Location: Wiltshire, England

PostPosted: Thu Oct 28, 2004 9:28 pm    Post subject: What is the best resolution for a scanned map? Reply with quote

Does anyone know what is the best resolution for a scanning a map? In other words what dpi (dots per inch) should I scan my map at? I want a good quality view but don't want to wast memory space on information I can't see in memory map.

Would have thought this was the most basic information that should be included in the help file?
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lbendlin
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Joined: 02/11/2002 22:41:59
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Location: Massachusetts, USA

PostPosted: Fri Oct 29, 2004 4:13 am    Post subject: Reply with quote

dpi is pretty irrelevant in this context. You should use as high of a resolution as you can afford (or your paper map yields). You are not measuring dpi but (tens of) yards per dot in real life. Your display device, however, is fixed at about 150 dpi

Have a look at Toporama, and compare their resolution to what you can achieve.
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TC
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Joined: Oct 22, 2003
Posts: 119
Location: Wiltshire, England

PostPosted: Fri Oct 29, 2004 9:38 am    Post subject: Reply with quote

Hi Lutz

Thanks for your reply. However I have to say that I absolutely disagree with you here. dpi is very important, it will determine how pixelated the map will be when displayed in Memory Map. High dpi values give good resolution (smooth, not pixelated) but consume memory space. Low dpi give small files but give a pixelated (blocky) appearance.

Obviously the act of calibration in memory 'stretches' the dots (pixels) to represent metres or yards. Hence high dpi means more pixels per yard, low means less pixels per yard

This implies there is a relationship between dpi and the scale the image is going to be 'stretched' to. So more properly, my question should have been what is the recommended dpi for scanning maps at various scales e.g.

1:100,000 = 200 dpi?
1:50, 000 = 150 dpi? etc.

Shoot me down if you disagree!

Thanks again
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lbendlin
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PostPosted: Fri Oct 29, 2004 1:59 pm    Post subject: Reply with quote

Can you estimate the quality of the paper map you are about to scan in? Is it 600 dpi, is it 4800 dpi? If you are scanning a 600 dpi paper map with 1200 dpi then this is obviously a waste of space. But if the paper map is high quality then you can also benefit from it and drive the final "yards per pixel" value down
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