QGIS

An Open Source Desktop GIS

Intro

Features

Cross-platform Lin/Win/Mac Desktop GIS
Works with Geospatial Standards
Written in C++
Embedded Python

Screenshot

Typical screen

Composer

Map Composer

C++

Development

Visualisation

Feature

Structure

Vector Layer

Structure

This is the structure of a vector layer

Feature methods

Method list

Python Console

Console

Python Editor

Console with Editor

Squirrels

Red and Grey

CC-licensed from flickr users imh and hisgett

Squirrels

Red and Grey

CC-licensed from flickr users king-edward and hisgett

Status

Distribution

What if populations triple and areas triple?
Can we buffer the regions and check for overlap?

Buffering

Options

Fixed Buffer

Styled...

How do we find a buffer width that scales an area?

Strategy

Binary Search

Area of buffer increases as width increases
Use a binary search algorithm to find w such that area of buffered region = S * area of region

QGIS Processing Scripts

Easy


##[BSR scripts]=group
##areas=vector
##scale_factor=number 2
##buffered=output vector

from PyQt4.QtCore import *
from qgis.core import *

import processing
from processing.core.VectorWriter import VectorWriter
from bsrutils import rescaleBuffer

areas_layer = processing.getobject(areas)
areas_features = processing.getfeatures(areas_layer)
fields = areas_layer.pendingFields().toList()
writer = VectorWriter(buffered, None, fields, POLYGON, areas_layer.crs() )

for feature in areas_features:
  outFeat = rescaleBuffer(feature, scale_factor)
  writer.addFeature(outFeat)

ui

Gets this

Run

and get

Conflict Area

Getting the conflict area

Split layer on attribute value
Intersection of those layers
Can we automate this?

Conflict processing script

outline


##[BSR scripts]=group
##areas=vector
##owner=field areas
##conflicts=output vector
...
for aFeature in features:
  for bFeature in features:
     if ownerValue(aFeature) != ownerValue(bFeature):
        if aFeature.geometry().intersects(bFeature.geometry()):
            outFeature.setGeometry(aFeature.geometry().intersection(bFeature.geometry()))
            writer.addFeature(outFeature)