GTECH 709 Databases Relational databases What makes a database geographic Geo-relational databases Locational references

Databases An organized collection of data A container of tables Each table has columns (“types”) Each table has a set of rows Every row has the same columns

Relational Databases Tables have relations that link data Relations mapping between a set of columns from table 1 to a set of columns of table 2 mapping can be implicit or explicit (foreign key) different types of relations: one-to-one one-to-many

Geo-relational Principle I don’t like to repeat myself but… To link two tables, they have to have a common identifier Label (column header) can be different Cell content must be a perfect match Mismatch examples “1000100” versus 1000100 “New York” vs. “NY” Matching addresses is particularly hard though it does make a user’s life easier

Shapefiles to Databases CartoDB imports shapefiles But stores the data internally in PostGIS QGIS default storage is a shapefile But it reads/writes many other formats ArcCatalog (ArcGIS) default is a geodatabase Logical organization of geographic data that practically comes in many different implementations

What Makes a Database Geographic What makes data geographic? Geographic data = space (+ time) + attributes From this week’s lab:

What Makes a Database Geographic What makes data geographic? Geographic data = space (+ time) + attributes From this week’s lab: attributes

What Makes a Database Geographic What makes data geographic? Geographic data = space (+ time) + attributes From this week’s lab: time

What Makes a Database Geographic What makes data geographic? Geographic data = space (+ time) + attributes From this week’s lab: space

Locational References How do we express locational references? Absolute versus relative Address (Nearest) point (Bounding) area GIS (for analytical purposes) requires these to be always in form of coordinates We will cover coordinate systems in two weeks Geometric (x,y) or geographic (lat,lon)

Locational Reference Encoding From our lab exercise this week: Remember: this is how we store geography We may then conveniently reuse coordinates to instruct GIS how to present them on a map