[Qgis-user] How to display a scale bar in km on a map in degrees?

[Carlos Cerdán]

Hi Barend:

You're right, Lat-long maps are just a plane representation of another
representation of Earth as an ellipsoid and fails on poles.

   > why not use UTM or another projection to start with?

Because some times we need simple maps, for example touristic maps of small
areas where you can forgot the ellipsoid and take Earth as plane. Examples
here:

- http://www.rumbosonline.com/images/issue13/13-64-map.jpg
-
http://www.kuelapadventure.com/spanish/index.php/tips-de-viajero/mapa-turistico-chachapoyas

A Lat-long grid would be useful to locate any place of these maps in Google
Earth but it's missed on both of them.

An UTM grid not always is a complete help. For example Where is the place
of next map: http://dynacorgold.com/en/casaden-overview-map-casaden.php
?  You have 60 options if you don't know what UTM zone is it.

If this is not sufficient for you... well I'll be wrong but I find useful
this kind of maps.

Thanks for the dissertation

Carlos




2013/4/16 <b.j.kobben at utwente.nl>

> Dear Carlos,
>
> I understand that you think the combination is useful, but my point is
> actually that the scale bar is NOT useful because it is plain wrong, it
> does not even approximate distances in many places in the map! Try
> wrapping you head around the fact that the North Pole (a single point of
> length 0 km) is actually shown as a line of the same length as the equator
> (40075 km), and you see how wrong your "approximate" distances can be....!
>
>
> And you do not answer my question: why not use UTM or another projection
> to start with? Latlon SEEMS simple, but many casual users fail to
> understand that they are actually looking at angles from the center of a
> Globe, plotted as if they are XY-coordinates on plain.
>
>
> And do not worry, your english is fine!
>
> Barend
>
> On 15-04-13 22:17, "Carlos Cerdán" <sig.upagu at gmail.com> wrote:
>
> >
> >
> >
> >2013/4/15 <b.j.kobben at utwente.nl>
> >
> >Hi there,
> >
> >I appreciate the clever tip for having a km scale bar on a lat-long maop,
> >but as a cartogra[her I must protest, because the scale bar is of course
> >mostly nonsensical. The differences in distances between the two (mercator
> >projected UTM and non-projected degrees) can potentially be huge. The
> >scale bar therefore cant be grossly wrong...
> >
> >
> >
> >Ajá.. As a simple user I find useful a scale bar to measure approximate
> >distances on a lat-long map.
> >
> >If you have your map in UTM, why not print that one with the proper scale
> >bar? The question to the original poster therefore would be: why do you
> >feel the need to have a map in degrees, why not use one that is projected
> >and where km is the proper scale-bar...?
> >
> >
> >
> >
> >In the same sense: If you want  to show the location of a place on Earth
> >to not GIS skills people, Lat-Long is useful for a first reading location
> >and scale bar to measure approximate distances ... so Why no use that
> >combination?
> >
> >
> >
> >Developers please fix an issue (Correct me if it's not an issue):
> >when you have two or more maps in a compositor and the scale bar is
> >related to map 1 (or more), and you close your file, next time you open
> >it, scale bar is related to Map 0 and you have to select Map 1 again.
> >(QGIS 1.8 - Ubuntu 12.04).
> >
> >
> >Carlos Cerdán
> >
> >
> >
> >PD Sorry if my English is bad.
> >
> >
> >
> >
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20130416/d6df3183/attachment.html>