Sources of Data, Metadata & FGDC

Federal Geographic Data Committee

Interagency committee in the US → develop policies, metadata standards, training. Supports National Spatial Dta Infrastructure

Spatial Data Infrastructure

• Clearinghouse (data-centric)

• Geoportal (service-centric)

How to prepare a GIS database?

• Why

• Goals

• Avoid exotic sources

• Accurate data

• Remember Law of Diminishing Returns

• Input different features onto separate data layers

• Each layer should be specific as possible

Cartographic objects

Digi rep of landscape features that are of interest to mapping

Attributes

Aspatial characteristics of cartographic objects that describe selected properties

Georelational data model e.g. shapefile

• Stores spatial & attribute data separately

• Links 2 via feature ID

Object-based data model e.g. geodatabase

Combines geometries and attributes in 1 system

Rows (records) rep…

Spatial features

Columns (fields) rep…

Characteristics

Different data types

Numbers, text/string, date, binary large object

Flat file

Contains all data in large table e.g. spreadsheet

Hierarchical database

• Organizes data at different levels

• Uses ONLY one-to-many

Network database

Build connections across tables

Relational database

Collection of tables that connect via keys (primary and foreign)

What is a “primary key”?

Unique ID

What is a “foreign key“?

Attribute tha1 match 1ary key in another table

+ve’s of Relational Model

• Table in database can be prepared, maintained, edited separately

• Tables can remain separate until query/analysis requires that attribute data from diff tables

Types of rls between records in tables

• one-to-one

• one-to-many

• many-to-one

• many-to-many

Joins

• Bring 2 tables together via common field

• For one-to-one or many-to-one

• NOT for one-to-many or many-to-many

Relates

• Temporarily connects 2 tables together via common field but physically separate

• Good for all 4 rls

• Bad because slows down data access

Spatial Join

Uses spatial rls to join 2 sets of spatial features & their attribute data