Shapefiles doubts

[Bart van den Eijnden (OSGIS)]

Hi,

many questions :-), some answers inline.

Best regards,
Bart

Apeksha Bhambhani wrote:

> Hiii all ,
>  
> These are the few doubts that we have , could somebody please help us .
>  
> 1.While writing the mapfile , we need to specify the extent of the map 
> . The background map chosen being in PNG image type , how do we get 
> the extent of this image , so as to enter this data in the mapfile .

Normally raster files have a file associated with them which contains 
the georeference information. For instance a tiff file is often 
associated with a tfw file. These files are also known as world files. 
If you just have a PNG file, there is no way to find out the extent from 
the file itself. Maybe the person who created the file knows, otherwise 
try to overlay the raster file with a vector file (roads, rivers etc. 
from the area) and determine common points, these are called GCP's or 
ground control points. If you have enough GCP's you can georeference the 
image using e.g. FWTools.

>  
> 2.In interactive web-mapping , do we need MySql to store the data of 
> the various points being plotted on the map or are the 
> shapefiles sufficient .
>  

What is your definition of interactive web-mapping? If your data is 
static, shapefiles are sufficient. If you need transactions, I would 
recommend using PostGIS as the datastore.

> 3. We are working on an online project and when a new point needs to 
> be plotted on the map and displayed , how can this data be entered 
> into the shapefiles . We have read somewhere that Mapscripting can be 
> used to convert textfiles to shapefiles .
> Can you please direct us as to how can that be done ???

As I said before, I would recommend using PostGIS instead and then you 
might use Geoserver on top as a transactional Web Feature Service (WFS). 
I don't know if this is within the scope of your project though. There 
is also a project in PHP which provides access directly to the PostGIS 
functions which can be found here:

http://avoir.uwc.ac.za/projects/postgis

>  
> 4. We have got to know about this book "Web mapping illustrated - By 
> Tyler Mitchell , O'reilly Publications " . Has anyone used used it for 
> developing an online interactive web-mapping apllication (example 
> editing of maps ).

I am a bit biased since I was one of the technical reviewers :-). It is 
a hands-on book which will teach you the basics for sure, but the main 
focus is not on Mapscript. Please note Mapserver is not focussed on 
editing, so the book is also not.

>  
> Thanks in advance ...................
>  
> Regards
> Apeksha
>
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-- 
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl