joshuapowell

joshuapowell

joshuapowell

SELECT 
	huc_6_name,   
	ST_AsGeoJson(ST_Multi(ST_Union(CAST(t.geometry AS Geometry)))) as huc_6_dissovled
FROM
	territory AS t
WHERE
	huc_6_name = 'Potomac'
GROUP BY
	huc_6_name

joshuapowell

SELECT
  r.id AS report_id, 
  t.id AS territory_id, 
  t.huc_12_name, 
  t.huc_10_name, 
  t.huc_8_name, 
  t.huc_6_name 
FROM 
  territory t, 
  report r 

joshuapowell

    CREATE EXTENSION postgis;


If this fails to run make sure GDAL is installed:

    apt-get install gdal-bin

joshuapowell

Import Millions of Features Into Mapbox

This tutorial assumes you have either a SHP file or GeoJSON file with your data ready to go and project at WGS1984 (i.e., 4326). It also assumes you are operating under a Unix environment.

Prerequisites

1. OGR
2. Brew
3. Tippecanoe
4. Mapbox.com Account

joshuapowell

## Convert your SHP File to a GeoJSON File
1. Download and Unzip your SHP file
2. Change to the SHP file directory
3. Convert the SHP file to a GeoJSON file
````
ogr2ogr -f "GeoJSON" my_file.geojson my_file.shp
````

## Convert your GeoJSON File to Mapbox Vector Tiles

joshuapowell

Effectively selecting colors for your choropleth map can be intimidating. Thankfully there are a couple of resources that can help us out.

The first is the ColorBrewer website which allows you to tinker with a preset or custom color pallette over a live map.

The second is a preconstructed D3 Map from the mbostock library that contains pre-defined colors, constructed using ColorBrewer.

http://mbostock.github.io/d3/talk/20111018/choropleth.html

joshuapowell

Download and Install Postgres.app

Before we can setup PostGIS we need to have a local version of Postgresql installed and running. The most effecient way to do this is to download and install Postgres.app.

Spatially Enable your Postgres Database

Once Postgres.app is installed in your computers /Applications directory. Open the Terminal and enter the following two commands

psql -d DATABASE_NAME -f /Applications/Postgres.app/Contents/Versions/9.3/share/postgresql/contrib/postgis-2.1/postgis.sql

joshuapowell

Virtualenv's bin/activate is Doing It Wrong

I'm a Python programmer and frequently work with the excellent [virtualenv][] tool by Ian Bicking.

Virtualenv is a great tool on the whole but there is one glaring problem: the activate script that virtualenv provides as a convenience to enable its functionality requires you to source it with your shell to invoke it. The activate script sets some environment variables in your current environment and defines for you a deactivate shell function which will (attempt to) help you to undo those changes later.

This pattern is abhorrently wrong and un-unix-y. activate should instead do what ssh-agent does, and launch a sub-shell or sub-command with a modified environment.

Problems