[GRASS-user] map resolution

Markus Neteler neteler at osgeo.org
Tue Nov 1 17:10:26 EDT 2011

```On Tue, Nov 1, 2011 at 4:53 PM, Chi Kit Lau <lau.chikit11 at gmail.com> wrote:
> Dear GRASS users,
>
> sorry for the beginner's question. How do I work out the maximum
> achievable resolution when rasterizing a vector map on a scale
> 1:10000? In other words what is the resolution of a map with a scale
> 1:10000?

This may be interesting for you

"Cartographic limitations [for vector maps]"
http://www.searchmesh.net/default.aspx?page=1817

Markus

PS: For raster maps, if you are using a scanner (adapted from
our GRASS book):

Suppose that the scale of the scanned map is 1:10,000. Thus, one centimeter
on the map is equivalent to 10,000cm on the ground.

Scan resolution, e.g. 300dpi:

300 lines                   lines
300dpi = ----------- = 118.11 ---------
2.54cm                      cm

Now we can calculate the on-ground distance that
corresponds to the length of a raster cell:

distance on the ground       10, 000cm                    cm                 m
---------------------------- = --------------- = 84.75 ------ = 0.85  ----
scanned lines per cm           118.11lines                   line
line

The resulting value of 0.85m is the spatial pixel resolution of the scanned
map at the 300dpi scan resolution. If you want the spatial resolution to
be an integer, do the inverse calculation and adjust the scanning resolution
accordingly.
```