Geocoding

Geocoding

• The process of transforming a description of a location—such as a pair of coordinates, an address, or a name of a place—to a location on the earth's surface
   
• An important step in spatial epidemiology

Address

2004 Mowry Road, 4th Floor, Gainesville, FL 32610

Street Number, Street Name, Street Type, Unit Number, City, Zip code

Source of Reference Map

• Topologically Integrated Geographic Encoding and Referencing (TIGER)
  -  developed by US Census Bureau
  -  free, nation-wide data
   
• TIGER include key features of geographic interest in the entire US:
  -  political boundaries
  -  lakes
  -  reservations
  -  major and minor roads, rivers, etc.

Enabling TIGER Geocoder within PostGIS

sudo -u postgres psql -c "CREATE EXTENSION fuzzystrmatch; CREATE EXTENSION postgis_tiger_geocoder;" phc6194spr18db

• Relies on string matching
  -  to find streets with similar spellings
  -  fuzzy-string-match extension

sudo -u postgres psql -c "GRANT USAGE ON SCHEMA tiger TO PUBLIC; GRANT USAGE ON SCHEMA tiger_data TO PUBLIC;
GRANT SELECT, REFERENCES, TRIGGER ON ALL TABLES IN SCHEMA tiger TO PUBLIC; GRANT SELECT, REFERENCES, TRIGGER ON ALL TABLES IN SCHEMA tiger_data TO PUBLIC;
GRANT EXECUTE ON ALL FUNCTIONS IN SCHEMA tiger TO PUBLIC; ALTER DEFAULT PRIVILEGES IN SCHEMA tiger_data
GRANT SELECT, REFERENCES ON TABLES TO PUBLIC;" phc6194spr18db

• Grant permissions to TIGER

Loading TIGER data

• PostGIS has several built-in functions that will generate scripts to download, decompress, and load TIGER data to database directly
   
• Steps:
  -  create a folder to store all the TIGER data
  -  generate scripts to download, decompress, and load data
  -  execute the scripts

Normalizing Addresses

• Address standardization / normalization:
  -  A preparatory step before geocoding is to parse the address into components such as street numbers, directional prefixes, street numbers, suffixes, etc.
   
• Normalizers:
  -  normalize_address
  -  pagc_normalize_address
  -  postal address geocoder

Geocoding

• Geocoding using address text:
  -  uses normalize_address function to normalize the address by deafult
  -  can also switch to pagc_normalize_address
   
• Geocoding using normalized addresses
   
• Batch geocoding

Lab: PostGIS TIGER Geocoder

git pull

Online Geocoding Service

Application Program Interface

• Application programming interface (API) is a set of subroutine definitions, protocols, and tools for building application software
   
• In general terms, it's a set of clearly defined methods of communication between various software components
   
• Common web service technologies:
  -  SOAP - Simple Object Access Protocol
  -  REST - Representational State Transfer

Google Geocoding API

• Documentation
   
• http://maps.googleapis.com/
  maps/api/geocode/json?sensor=false&address=
  Gainesville%2C+FL

Security and Rate Limiting

• The data provided by these APIs is usually valuable
   
• The data providers might
  -  limit the number of requests per day,
  -  or demand an API "key",
  -  or charge for usage

Lab: Google Map Geocoding API

https://developers.google.com/maps/documentation/geocoding/start

Increase the limit here: e.g. 1000