Mathare Building import

From Map Kibera

In this page, I (Sébastien) will describe how to import the data of the building extraction of Mathare that we've got from AAAS. See Primož's blog for the initial analysis.

Contents 1 Changing the SRS 2 Setup PostGIS database 3 Import the shapefiles to the db 4 Import OSM data to the db 5 Find collisions between OSM and the import candidate 6 Tagging scheme 7 Generate the OSM data to be imported

Changing the SRS

The data was made available as shapefiles in WGS84 Web Mercator Auxiliary Sphere projection, which is known as Web Mercator, spherical Mercator, Google Mercator and is referenced by various ids: EPSG:900913, EPSG:3785 (obsolete), EPSG:3857, ESRI WKID 102100... In QGIS, it's known as Google Mercator, EPSG:900913, ID 3644.

Before working with the data, we need to change the Spatial Reference System (SRS) to be compatible with OSM, that is moving to non-projected WGS84.
In QGIS: menu Vector -> Data Management Tools -> Export to new projection. Then choose the output CRS to be WGS84, EPSG:4326, ID 3452.
The two files that we're going to import are GroundTruthed-wgs84.shp and BuildingsOnTop-wgs84.shp

Setup PostGIS database

PostGIS is relatively easy to install on Ubuntu. I might describe it further later. Anyway, the current environment is PostgreSQL 8.4, PostGIS 1.5.
I found this script from GeoDjango very convenient to create a postgis db template:

$ ./create_template_postgis-debian.sh
$ createdb -T template_postgis mathare

Import the shapefiles to the db

Import OSM data to the db

Find collisions between OSM and the import candidate

Tagging scheme

Generate the OSM data to be imported