Get some data and import it

Grab populated places points

wget http://edcftp.cr.usgs.gov/pub/data/nationalatlas/citiesx020.tar.gz

Grab US counties map:

wget http://edcftp.cr.usgs.gov/pub/data/nationalatlas/countyp020.tar.gz

Lots more data available in the National Atlas

Extract shapefiles from the two archives

tar -xzvf citiesx020.tar.gz
tar -xzvf  countyp020.tar.gz

Ogrinfo the files to have a look at them

ogrinfo citiesx020.shp
INFO: Open of `citiesx020.shp'
      using driver `ESRI Shapefile' successful.
1: citiesx020 (Point) 

ogrinfo countyp020.shp
INFO: Open of `countyp020.shp'
      using driver `ESRI Shapefile' successful.
1: countyp020 (Polygon)

Notice that the cities shapefile is a point layer and the county layer is a polygon layer.

Import the two shape files into your PostGIS db

To get started with PostGIS see my first tutorial.

ogr2ogr -f "PostgreSQL" -s_srs EPSG:4269 "PG:dbname=mydbname" countyp020.shp -nln us_counties
ogr2ogr -f "PostgreSQL" -s_srs EPSG:4269 "PG:dbname=mydbname" citiesx020.shp -nln us_cities

Make sure you change mydbname to your database’s name.

Checking the Import

psql mydbname
mydbname# \d us_cities
                                   Table "public.us_cities"
    Column    |       Type       |                          Modifiers
--------------+------------------+-------------------------------------------------------------
 ogc_fid      | integer          | not null default nextval('us_cities_ogc_fid_seq'::regclass)
 wkb_geometry | geometry         |
 citiesx020   | double precision |
 feature      | character(27)    |
 name         | character(48)    |
 pop_range    | character(21)    |
 pop_2000     | numeric(8,0)     |
 fips55       | character(5)     |
 county       | character(55)    |
 fips         | character(5)     |
 state        | character(2)     |
 state_fips   | character(2)     |
 display      | numeric(1,0)     |
Indexes:
    "us_cities_pk" PRIMARY KEY, btree (ogc_fid)
    "us_cities_geom_idx" gist (wkb_geometry)
Check constraints:
    "enforce_dims_wkb_geometry" CHECK (ndims(wkb_geometry) = 2)
    "enforce_geotype_wkb_geometry" CHECK (geometrytype(wkb_geometry) = 'POINT'::text OR wkb_geometry IS NULL)
    "enforce_srid_wkb_geometry" CHECK (srid(wkb_geometry) = -1)

You can see that ogr2ogr has imported the shapefile, created a primary key (ogc_fid) and created a spatial index. What you can’t see is that ogr2ogr was also nice enough to add an entry to the geometry_columns table so that postgis tools know that there is a geometry column (wkb_geometry) in this table.

Looking at the Data

Lets fire off qgis and see what we have

Next time, querying with spatial predicates….I promise it won’t take six months for the next post.

mkdir ${HOME}/macports
cd ${HOME}/macports
wget http://svn.macports.org/repository/macports/downloads/MacPorts-1.6.0/MacPorts-1.6.0.tar.gz
tar -xzvf MacPorts-1.6.0.tar.gz
cd MacPorts-1.6.0
./configure --prefix=${HOME}/macports --with-tclpackage=${HOME}/macports/tcl \
--with-install-user=${USER} --with-install-group=${USER}
make
make install

You will now have a macports directory in your home directory:

$ ls macports
bin     etc     include lib     libexec man     sbin    share   src     tcl     var     www

Add ${HOME}/macports/bin to your path and you’ll be able to run “port install *portname*” ports you install will get installed in your home directory. Handy for any little tools you need to have available that might not be built on the system you’re using.

sudo apt-get install gdal-bin

Once you have GDAL/OGR installed you get a slew of command line utilities, I’ll try to cover some others in later tutorials, but for now we’re interested in ogr2ogr. ogr2ogr converts between the vector formats that OGR understands.

Example using a shapefile at the city of chicago website:
Download the data

wget http://egov.cityofchicago.org/webportal/COCWebPortal/COC_ATTACH/TIFS2008.zip

Unzip it

unzip TIFS2008.zip

Now we have to do the hard part (not really that hard, but important), look for the projection information in the metadata. I looked in the tifs.shp.xml file and found that the projections is:

NAD_1983_StatePlane_Illinois_East_FIPS_1201_Feet

Google uses WGS84 spatial reference system.
Now we have to lookup EPSG codes that OGR understands for these projections. A good spot to do this is spatialreference.org. EPSG codes provide a short form of expressing projection and spatial reference information.
Once we have that all sorted out we’re ready to run ogr2ogr:

ogr2ogr -f "KML" -s_srs "EPSG:102671" -t_srs "EPSG:4326" tifs.kml tifs.shp

The -f “KML” specifies that we want the output in KML. -s_srs is the source (tifs.shp) spatial reference system and -t_srs is the target spatial reference system found at spatialreference.org, then we specify the output file tifs.kml and the input file tifs.shp. That is it!

Lets shrink it down into a kmz (compressed kml) so that it takes up less disk space.

zip tifs.kmz tifs.kml

This is my linux config file (~/.synergy.conf), create one if it doesn’t exist

section: screens
  laptop:
  desktop:
end
section: links
laptop:
  right = desktop
desktop:
  left = laptop
end

(adjust to suit your needs)

The documentation is pretty good, so this should get you started.

Then I connect using synergyc:

synergyc --name laptop xxx.xxx.xxx.xxx

where xxx.xxx.xxx.xxx is the name of the computer with the server running on it.

As you can see there is no security to speak of keeping others from controlling your system’s mouse and keyboard, so on hostile networks it is probably best to block the port and tunnel over ssh.

This would be great to set up an ad-hoc multi-head system when getting together with colleagues to work collaboratively with a bunch of laptops. Haven’t tried that yet, but it would be pretty slick.