Data Bases: Population and Maintenance

1
Data Bases Population and Maintenance

• Geog 176B Lecture 8

2
Data Collection

• One of most expensive GIS activities
• Many diverse sources (source integration, data
  fusion, interoperability)
• Two broad types of collection
• Data capture (direct collection)
• Data transfer
• Two broad capture methods
• Primary (direct measurement)
• Secondary (indirect derivation)

3
Stages in Data Collection Projects
4
Data Collection Techniques
Raster Vector
Primary Digital remote sensing images GPS measurements
Primary Digital aerial photographs Survey measurements
Secondary Scanned maps Topographic surveys
Secondary DEMs from maps Toponymy data sets from atlases
5
Primary Data Capture

• Capture specifically for GIS use
• Raster remote sensing
• e.g. SPOT and IKONOS satellites and aerial
  photography
• Passive and active sensors
• Resolution is key consideration
• Spatial
• Spectral
• Temporal

6
www.spot.ucsb.edu
7
Imagery for GIS
8
Vector Primary Data Capture

• Surveying
• Locations of objects determines by angle and
  distance measurements from known locations
• Uses expensive field equipment and crews
• Most accurate method for large scale, small areas
• GPS
• Collection of satellites used to fix locations on
  Earths surface
• Differential GPS used to improve accuracy

9
Total Station
10
Pen/Portable PC and GPS
11
Secondary Geographic Data Capture

• Data collected for other purposes can be
  converted for use in GIS
• Raster conversion
• Scanning of maps, aerial photographs, documents,
  etc
• Important scanning parameters are spatial and
  spectral (bit depth) resolution

12
Scanner
13
Raster to vector conversion
14
Vector Secondary Data Capture

• Collection of vector objects from maps,
  photographs, plans, etc.
• Digitizing
• Manual (table)
• Heads-up and vectorization
• Photogrammetry the science and technology of
  making measurements from photographs, etc.

15
Digitizer
16
Data Transfer

• Buy vs. build is an important question
• Many widely distributed sources of GI
• Includes geocoding
• Key catalogs include
• Geodata.gov
• Geography Network
• Access technologies
• Translation
• Direct read

17
Managing Data Capture Projects

• Key principles
• Clear plan, adequate resources, appropriate
  funding, and sufficient time
• Fundamental tradeoff among
• Quality, accuracy, speed and price
• Two strategies
• Incremental
• Blitzkrieg
• Alternative resource options
• In house
• Specialist external agency

18
A useful rule of thumb is that positions measured
from maps are accurate to about 0.5 mm on the
map. Multiplying this by the scale of the map
gives the corresponding distance on the ground.
 
19
Positional Accuracy (cont.)

• within a database a typical UTM coordinate pair
  might be
• Easting 579124.349 m
• Northing 5194732.247 m
• If the database was digitized from a 124,000 map
  sheet, the last four digits in each coordinate
  (units, tenths, hundredths, thousandths) would be
  questionable

20
Testing Positional Accuracy

• Use an independent source of higher accuracy
• find a larger scale map
• use precision GPS
• Use internal evidence
• digitized polygons that are unclosed, lines that
  overshoot or undershoot nodes, etc. are
  indications of error
• sizes of gaps, overshoots, etc. may be a measure
  of positional accuracy

21
Testing Accuracy (cont.)

• Compute accuracy from knowledge of the errors
  introduced by different sources
• e.g., 1 mm in source document
• 0.5 mm in map registration for digitizing
• 0.2 mm in digitizing
• if sources combine independently, we can get an
  estimate of overall accuracy...

22
Definitions

• Database an integrated set of data (attributes)
  on a particular subject
• Geographic (spatial) database - database
  containing geographic data of a particular
  subject for a particular area
• Database Management System (DBMS) software to
  create, maintain and access databases

23
A GIS links attribute and spatial data

• Attribute Data
• Flat File
• Relations

• Map Data
• Point File
• Line File
• Area File
• Topology
• Theme

24
Advantages of Databases over Files

• Avoids redundancy and duplication
• Reduces data maintenance costs
• Faster for large datasets
• Applications are separated from the data
• Applications persist over time
• Support multiple concurrent applications
• Better data sharing
• Security and standards can be defined and
  enforced

25
Disadvantages of Databases over Files

• Expense
• Complexity
• Performance especially complex data types
• Integration with other systems can be difficult

26
Types of DBMS Model

• Hierarchical
• Network
• Relational - RDBMS
• Object-oriented - OODBMS
• Object-relational - ORDBMS

27
Relational Databases rule now
28
Characteristics of DBMS (1)

• Data model support for multiple data types
• e.g MS Access Text, Memo, Number, Date/Time,
  Currency, AutoNumber, Yes/No, OLE Object (MS
  Object linking and embedding), Hyperlink, Lookup
  Wizard
• Load data from files, databases and other
  applications
• Index for rapid retrieval

29
Characteristics of DBMS (2)

• Query language SQL
• Security controlled access to data
• Multi-level groups (e.g. census, NGA)
• Controlled update using a transaction manager
• Versioning
• Backup and recovery

30
Characteristics of DBMS (3)

• Applications
• Forms builder
• Reportwriter
• Internet Application Server
• CASE tools
• Programmable API (Applications program interface)

31
Role of DBMS
Task
System

• Data load
• Editing
• Visualization
• Mapping
• Analysis

Geographic Information System

• Storage
• Indexing
• Security
• Query

Database Management System
Data
32
Relational DBMS (1)

• Data stored as tuples (tup-el), conceptualized as
  tables
• Table data about a class of objects
• Two-dimensional list (array)
• Rows objects
• Columns object states (properties, attributes)

33
Table
Column attribute
Row object Vector feature
34
Relational DBMS (2)

• Most popular type of DBMS
• Over 95 of data in DBMS is in RDBMS
• Commercial systems
• IBM DB2
• Informix
• Microsoft Access
• Microsoft SQL Server
• Oracle
• Sybase

35
SQL

• Structured (Standard) Query Language
  (pronounced SEQUEL)
• Developed by IBM in 1970s
• Now de facto and de jure standard for accessing
  relational databases
• Three types of usage
• Stand alone queries
• High level programming
• Embedded in other applications

36
Types of SQL Statements

• Data Definition Language (DDL)
• Create, alter and delete data
• CREATE TABLE, CREATE INDEX
• Data Manipulation Language (DML)
• Retrieve and manipulate data
• SELECT, UPDATE, DELETE, INSERT
• Data Control Languages (DCL)
• Control security of data
• GRANT, CREATE USER, DROP USER

37
Relational Join

• Fundamental query operation
• Occurs because
• Data created/maintained by different users, but
  integration needed for queries
• Table joins use common keys (column values)
• Table (attribute) join concept has been extended
  to geographic case

38
Join
1241 Ford 2003
1241 Subaru 2000
1241 Honda 1999
Record ID Address cars
1241 123 State St. 3
1242 1801 Main St. 1
1243 2106 Elm St. 2
1244 7262 Pine Drive 1
1241 123 State St. Ford
1241 123 State St. Subaru
1241 123 State St. Honda
1242 1801 Elm St. Kia
39
Spatial indexing

• Many maps tiled
• B-tree (Balanced)
• Grid indexing
• Quad tree Points/regions
• R-tree (Based on MBR)

40
New global/spatial grids QTM
41
Go2 Grids
385322.08N 0770206.86W US.DC.WAS.54.18.28.83.1
1 US.CA.SBA.UCSB.UCEN
42
Spatial SearchGateway to Spatial Analysis

• Overlay is a spatial retrieval operation that is
  equivalent to an attribute join.
• Buffering is a spatial retrieval around points,
  lines, or areas based on distance.