[Qgis-user] Converting gif/jpeg images to shape files

[Mick]

On Mon, 27 Jun 2011 22:29:56 +0200
Andreas Neumann <a.neumann at carto.net> wrote:

> Hi,
> 
> What is the purpose of converting these maps to vector files?
>  I doubt that it makes a lot of sense to convert scanned historic maps
> to a vector format (unless it is clearly a clean black and white line
> graphic).

Included in the historic rasters is parts of features, eg canals,
turnpikes, etc, that have been omitted from the OS OpenData set I am
using for base layers.

> 
> You will get all sorts of ugly artefacts and the filesize would
> probably be bigger than the original rasters. Also, you would get
> vectors without attribute data (except maybe color/gray values),
> which is also not ideal.

Artifacts I can fix and attributes I can add, it just takes time. File
size isn't an issue at this stage.
> 
> Probably you just want to geo-reference those scanned maps and use
> them as background layers?
> 
> Andreas
> 
As an Invalid Pensioner I am time-rich - money-poor so the time
involved is not a serious concern. The goal of my project is to produce
a set of map layers depicting the world my ancestors lived in (1600 -
1840) that I can share with other family historians.

The desired results are a set of maps that can be shared as either ESRI
shape files, MapInfo tables or Google Earth overlays.

mick