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 43E, 12S on

December 2, 2002 was 32C”; geographic fact - “Mount Kilimanjaro is 5000m high” ? - “Zanzibar City center is situated at 44E, 1130’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 GeographyConceptual 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 GeographyConceptual 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 GeographyDigital 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 GeographyDigital 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 GeographyRelationship: Conceptual/Digital

In principle

In practical there is strong association

Raster

Vector

CodeObjects

Fields

Raster

Vector

Objects

Fields

Code

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”

SEARCHActivity-ID (PK/FK)Source-ID (FK)Repository-ID (FK)Researcher-ID (FK)Searched-For

REPOSITORYRepository-ID (PK)Place-ID (FK)NameAddressPhoneHoursComments

REPOSITORY-SOURCERepository-ID (FK)Source-ID (FK)Activity-ID (FK)Call-Number (This copy)Description

SOURCE-GROUP-SOURCESource-ID (FK)Source-Group-ID (FK)

SOURCESource-ID (PK)Higher-Source-ID (FK)Subject-Place-ID (FK)Jurisdiction-Place-ID (FK)Researcher-ID (FK)Subject-DateMediumComments

SOURCE-GROUPSource-Group-ID (PK)Source-Group-Name

EVIDENCE

Operactional

GIS

GIS Users

Levels of data model abstraction

Reality

Conceptual Model

Logical Model

Phisical Model

Human-Oriented

Computer-Oriented

Increase abstraction

Real-world phenomena

Partially model of objects

Implementation-orientad

GIS application

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).

- Data load

- Editing

- Mapping

- Analysing

- Store

- Indexing

- Security

- Query

Geographic Information system

Object Relational Database management system

Data

The roles of GIS and DBMS Tasks

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.