[postgis-users] Postgresql, postgis and PHP

[Louwrens du Toit]

Dear Postgis-Users List,

I'm an experienced web developer (mainly PHP, Javascript, MySQL) and 
have recently started a job where I need work with geographic 
information, mainly in a Postgresql database. So, I'm quite new to all 
this geographical data etc and have a few questions:

So, I have a database (Postgresql) with geographical data (mainly 
polygons in format "geometry" - srid 4326). Now I can do some area 
(ST_Area) and intersection (ST_Intersection) queries but would like to 
know the following:

1. I have several tables with polygon data (layers) but need to do 
queries across them (what I need to do in the end is to create charts - 
bar,pie etc). I.e I would like to know for instance, what percentage 
area of layer 1 falls within the area in layer 2? or
2. I have raster data (in geotiff format), and would like to know... per 
polygon (in layer 1 above), what is the mean value of the raster data...

Can someone point me in a direction of where to information like this. 
How should I go about this problem?

I hope this makes sense. As I said, I'm very new to all this geographic 
stuff.

Thank you,
LJ du Toit

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LJ du Toit