Transcript GIS Presentation G2

GIS presentation g2
Contents:
 Representing Geography -Yahya
 Geographic data models – Zeferino
 Creating and maintaining geographic databases –
Nima & Lucia
 DHIS & GIS in Mozambique - Leopoldo
Representing Geography
 All human activities require knowledge about
the earth.
- representations help us get that knowledge.
- we use it for planning. where to get/keep…
 Digital presentation has many advantages
over the others.
- data are easy to process, transform and
analyze, easy to copy and transmits.
- maps can change scale, zoom, pan. no sheet
boundary limitations!
Representing Geography contd
 Concerned with the earth’s surface or near surfaces.
- Represent every thing? No. a key issue is what and
how.
- useful if it is accurate.
 Geographic data link place, often time and attributes
- “The temperature at Dar es salaam 43E, 12S on
December 2, 2002 was 32C”; geographic fact
- “Mount Kilimanjaro is 5000m high” ?
- “Zanzibar City center is situated at 44E, 1130’S
and is 3m above sea level” !
Data used fictitious!
Representing Geography Attributes
 Classified as nominal, ordinal, interval, ratio.
 Nominal: identifies one entity from another; e.g. place
names; no comparison/relationship can be made.
 Ordinal: values have natural order; e.g. soil classes;
class1, class2,…. “class2 is between class1 and 3”!
 Interval: differences make sense; e.g. temperatures.
 Ratio: ratio make sense; e.g weight. What about
temperature?!
Representing Geography
Conceptual representation
Two ways: Discrete objects and Fields
 Object view: the world is empty except where it is occupied
by objects with defined boundaries.
- e.g a district is littered with PHCs, roads, population
- identified by dimension; points, lines, polygons.
- information can be expressed in tables; objects with
attributes.

Consider a terrain, composed of peaks, valleys, ridges,
slopes, etc… Do we count them? Do we list them?

Useful to think of terrain as a continuous surface
- elevation defined rigorously at every point.
Field view!
Representing Geography
Conceptual representation
 Field view: real world represented as finite numbers of
variables, each one defined at every possible position
 Differences: objects/fields
- Objects distinguished by their dimensions;points,
lines, areas.
- Fields distinguished by what varies and how
smoothly.
Field or object?
- Population density
- Himalaya mountains
- Al-Rahma Hospital in Zanzibar.
Representing Geography
Digital representation
 Two methods: raster and vector.
 Raster: represent the world into arrays of cells and
assign attributes to the cells.
- laying of tile floor on a flat surface
- the earth is not flat. Discussion section 4.7
- sources: remote sensing satellites, imagery
- applied: resources, environmental planning
- fixed resolution
- volume of data depends on cell size
- represent more honestly
Representing Geography
Digital representation
 Vector: lines are captured as points connected by
precisely straight lines. An area is made of vertices
connected by straight lines.
- volume depends on density of vertices
- used for social, economic and administration.
- source: social, environmental
- variable resolution
Representing Geography
Relationship: Conceptual/Digital
In principle
Code
Raster
Objects
Fields
Vector
In practical there is strong association
Raster
Vector
Code
Objects
Fields
Representing Geography paper maps
 Represent the world in two dimensions.
- meaningful scale
- true maps
- static
 Challenge: paper maps are useful metaphors for the
contents of a geographic database, but lets think
more on better ways of geographic representation.
Presented by: Yahya El Hamad
Geographic Data
Modeling
What is a data model?
”Set of construct for describing and representing selected
aspects of the real-world in a computer”
SOURCE-GROUP
SOURCE-GROUPSOURCE
Source-Group-ID (PK)
Source-Group-Name
Source-ID (FK)
Source-Group-ID (FK)
SEARCH
Activity-ID (PK/FK)
Source-ID (FK)
Repository-ID (FK)
Researcher-ID (FK)
Searched-For
EVIDENCE
REPOSITORYSOURCE
SOURCE
Source-ID (PK)
Higher-Source-ID (FK)
Subject-Place-ID (FK)
Jurisdiction-Place-ID (FK)
Researcher-ID (FK)
Subject-Date
Medium
Comments
At
le
as
t
on
e
Repository-ID (FK)
Source-ID (FK)
Activity-ID (FK)
Call-Number (This copy)
Description
Operactional
REPOSITORY
Repository-ID (PK)
Place-ID (FK)
Name
Address
Phone
Hours
Comments
GIS
GIS
Users
Levels of data model abstraction
Reality
Increase
abstraction
Conceptual Model
Logical Model
Implementationorientad
Phisical Model
GIS application
Real-world
phenomena
HumanOriented
Partially model
of objects
ComputerOriented
Models
 1. CAD data Model
 Systems real-world entities are represented
symbolically as simple point, line, and polygon
vectors.
 Tipical use local drawing coordinate instead of
real-world coordinate for representing objects.
 Individual objects a represented with unique
identify.
Models (2)
 2. Raster data Model
 Uses an array of cells, or pixels to
represent real-world objects
 Store multiple atributes for each cell in a
type of value attribute table.
 The array itself is stored as a compressed
file or as a record in a database.
Models (3)
 3. Vector data Model
 Each object in the real-world is
classified into a generic type: point,
line, or polygon.
 The coordinates that difine the
geometry of each object may have 2,
3, or 4 dimensions.
Models (4)
4. Object data Model
•Real-world is modeled as a collection of geographic objects
and its relationship.
•Each entity in the real-world to be included in the GIS is an
object.
•Objects of same type are grouped toghether as object
classes.
•Each object class is stored in form of a database table.
CREATING AND MAINTANING
GEOGRAPHIC DATABASES
GEOGRAPHIC DATABASE
 Database
 Geographical database
 Advantage of database approach over file
based systems:data sharing, security, data
independence, data centralization
DATABASE MANAGEMENT
SYSTEM(DBMS)
 Database Management System: The
software which were created for the
purpose of creating database, manage
database and control access to the data.
TYPES OF DBMS
 RDBMS - Relational Database Management system
eg DB2,Informix Dynamic server,Microsoft Access,
sql server , oracle universal server etc.
 ODBMS - Object oriented DBMS store objects
persistently, eg objectstore, gemstone.
 ORDBMS - Relational database adapted to handle
objects. Example Oracle spatial option,Informix
spatial datablade etc.
RDBMS
 Problems:
- Inability to store complete object directly
in
the database (object state and
behaviour).
- Couldn’t process rich data types such
geographic objects (maps, shapes etc).
- Poor perfomance (speed, complex
structure).
The roles of GIS and DBMS
Geographic Information
system
Tasks
- Data load
- Editing
- Mapping
- Analysing
Object Relational
Database management
system
- Store
- Indexing
- Security
- Query
Data
Storing data in DBMS
 Layer is a organised collection of data
on a particular theme such as roads in
certain district in Mozambique, health
posts in Gaza Province
 Database design- Normalization
rule(codd (1970))
Achieving simple tables structure which
has disadvantage of poor perfomance
and complex structure
SQL
 Designed specifically for database
 Two types of SQL statements:
- Data Definition Language(DDL):
used to create, alter and delete DB
structure eg CREATE, ALTER,DROP
- Data Manipulation Language
(DML): Used to manipulate and retrieve
data eg Select, update, delete
STRUCTURING GEOGRAPHIC INFORMATION
 The aim is to improve efficiency(speed) of
querying, analysing and mapping
 Two types
 Topologic - create a topology for vector
datasets using either batch or interactive
techniques.This can help to speed up in
certain types of queries
 Indexing database
Editing and Data Maintenance
- Process of making changes to GDB by adding new
objects or changing existing objects
- In Gis we have tools for creating and editing
Geographic objects geometric and attributes
eg object coordinates can be added to GDB digitizing
tables, survery etc
In multiple user environment we have to take control of
concurrent access problem.