DATA
• Spatial Data – where things are
• Non Spatial Data or Attribute Data – What
things are
• Data in a computer database are managed and
accessed through a DataBase Management System
(DBMS)
• The DBMS allows users to deal with data without
needing to know how the data are stored and
structured in the computer.
Database Concepts
• GIS creates a model of the world
• GIS uses raster and vector representations
(spatial data) to model location of
geographic features
• All geographic features are linked to non
spatial data or attributes that describe or are
related to the spatial data/features.
Database Creation
• Data investigation – What
do you need to know?
• Data modeling – conceptual model by examining the
relationships between features (entities) and the the
characteristics of the features/entities (i.e. attributes)
• Database design – field names, types and structure
along with the DBMS
• Database implementation – populating the fields, fine
tuning, updating, etc.
Advantages of computer-based
databases
• Different data access methods are possible.
• Data are stored independently of the application
for which they will be used.
• Redundancy will be minimized.
• Access to data can be controlled (passwords)
• Database is relatively easy to maintain and
updating is possible
• Standardized query languages can be used.
GIS Links features to their attributes
Managing Non-spatial data
Flat Files or Spread Sheets
•Each geographic feature is matched to one row “record” of data.
•All records in this database have the same number of “fields”
(columns in GIS databases are called fields, rows are called records)
•When the number of fields becomes lengthy a flat file
is cumbersome to search.
Managing Non-spatial data
Hierarchical files
Hierarchical files
Hierarchical files
store data in more
than one type of
record, “one to
many”
relationship.
One field is key to
all records, but
data in one record
does not have to be
repeated in
another.
Managing Non-spatial data
Relational Files
• Connects different files or tables without using
internal pointers or keys. Instead a common link
of data is used. A “matrices of tables” is used to
store the information.
Stock Inventory
Reorder item
Targeted marketing
by zip code
GIS Database
Scan bar code
Purchase
Lamp at
Pier 1
Imports
Scan credit card
Debit authorized
Profile on your buying habits
We are an information producing society and information
is worth lots of $$$
Structured (Standard) Query
Language
• Database queries through the SQL of DBMS
–
–
–
–
Sorting
renumbering
Searching
Subsetting
• This allows for the creation of new data
• Geographic search is the key of GIS
• Which customers from the 93940 zip code spent over
$100 in 2001?
Tabular data compatible with
ArcView
• dBASE (.dbf) use dBASE IV but III works
too.
• Delimited text
• INFO format (ARC/INFO)
• ArcView can also link to DBMS like
Ascess, Visual FoxPro, Excel, dBASE
ArcView Table data types
•
•
•
•
Short and Long Integer (13252637)
Text (afdje83kfur74)
Date (based upon standard time format)
Object ID, Float, Double, Blob
How projects and files are stored
in ArcView
File extentions
•
•
•
•
•
•
•
Project.mxd is an ArcView Project file
Filename.shp
Filename.shx
Filename.dbf
.ain and aih (table has been linked)
.sbn and .sbx (table has been joined)
(.avi a script has been added – ArcView 3.2)
Joining Tables
• To join a table you need a common attribute
field.
• A table join is preserved only within a map
document, the table on disk are not
changed. To permantly append – export as a
data set.
• One to one or many to one relationships
• See page 224 in GTKArcGIS
Relating Tables
• One to many relationship
• One record in the attribute layer table
relates to many in the Non-spatial table.