introduction to gis used to describe computer facilities which are used to handle data referenced...
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INTRODUCTION TO GEOGRAPHICAL INFORMATION
SYSTEM
INTRODUCTION TO GIS
Used to describe computer facilities which are used to handle data referenced to the spatial domain.
Has the ability to inter- relate datasets and to carry out functions to improve their analysis and the presentation of the results.
DEFINITON OF GIS GIS is defined as
“ a set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes.”
A computerized system for capturing, checking, manipulating analyzing and displaying data related to positions on or near the earth’s surface.
EVOLUTION (from mapping to GIS) Topological technique permitted the data not
only to determine where a point or a line or an area was located but also to analyze those features.
GIS data can be assembled by
-existing databases
-digitized or scanned from existing maps
-GPS surveying techniques
DEVELOPMENT WITH MODERN GIS Modern GIS developments are based on a data
theory.
There are several aspects are considered:GIS specific characteristic
a) location-coordinates and street address
b) attributes-features that being analyzed
GIS activities can be by two board field
a) geographic
b) cultural
ADVANTAGES of GIS
Storage and easily update data Sort and store spatial features Allow to zoom into section of data to graphic
and text which may be hidden Analyze both entities and data using
sophisticated computer programs Allow user to prepare maps
Allow user to use data to prepare maps at different scales
Allow to import stored data electronically and save the cost of collecting data
Build and augment a database Create new maps by modeling or reinterpreting
existing data
COMPONENTS OF A GIS It can be divided into 4 major activities:
- Data collection and input.
- Data storage and retrieval.
- Data analysis.
- Data output and display.
GIS FUNCTIONAL ELEMENTSData
Collection and Input
Digital
Data Storage and Managemen
t
Data Retrieval
Data Manipulation and Analysis
Data Display
Image Copy
Hard Copy
GIS TYPICAL COMPONENTS: The computer with GIS software is the main
component and typically uses Microsoft or Unix operating systems.
Data collection can be divided into geometrics components that are:
- Field surveying,
- Remote sensing,
- Digitalization of existing maps and plans,
- Digital data transfer via Internet or CD/DVD
Computer storage:
- Hard disks,
- Optical disks etc. Software designed are to download, edit, sort and
analyze data. It also designed to process and present data in the
form of graphics and maps and/or plans.
SOURCES FOR GIS DATA: The most important part of GIS is the collection of
data. If data can be obtained from other sources, the
efficiency of the process increases.
Traditional sources for data collection:
- Field surveying.
- Remotely sensed images.
- Existing topographic maps, plans etc.
- Electronic transfer of previously digitalized data from Government agencies or commercial firms.
DATA SOURCES
GIS
DATA SOURCE
S:Structur
al, Construction,
Hydrology,
Environmental.
DATA MANIPULATION:Highwa
y design,
Site plannin
g, Landsca
pe plannin
g, Drainag
e analysis
.
DATA CATEGORISATIONNode Arc Polygon
• point Independent arc Independent single polygon
Independent multiple polygon
• point with vertical information
Independent multiple arcs
Contiguous polygon
Point in polygon
• arc junction Connected arcs network
overlap noncontiguous
GIS DATA STRUCTURE
GIS data structure can be divided into
Spatial data
Attribute data
GIS DATA STRUCTURE
Spatial
Vector data
format - positional data is represented
in form of
coordinates
Raster data
format – consists of a set
or matrix of cells or pixels of a specific
size and area.
Attribute
Digital data- record data by using
computer software. Example computer
programming
Non- Digital date – record data by
writing manually.
Example file.
In vector data format, the basic unit of spatial information are points, lines and areas.
Each units is composed as a series of one or more coordinate points.
By using vector systems, there are 3 types of objects possible:NodesArcsPolygons
VECTOR DATA FORMAT
RASTER DATA FORMAT Consists of a set or matrix of cells or pixels of a
specific size and area.
The image represent a scanned map or an aerial
photograph of the site to be modeled.
Point is represented by a single grid cell, a line by
consecutively neighboring cells and an area by a cluster
of neighboring cells.
Can be for merging and investigating the vectorising
method for a specific purpose
Example : raster image with a vector image for movement of river
COMPARISON OF VECTOR AND RASTER
VECTOR DATA RASTER DATA
Represent feature shape more accurately Rectangular representation and more
generalized.
Represent feature with well- defined
boundaries.
Represent a more generalized view.
Compact data structure represented by
simple points, lines and polygons with
topological relationship.
The data structure relatively simple. It uses
rows and column of grid cell having uniform
size.
Resolution of data depends on compilation
method and scale of source data.
The data resolution depends on the cell size.
Easy to represent topological relationships. Difficult to represent topological
relationships.
GEOREFERENCING: Most geographic data users have the same earth-
reference techniques that the data can be shared by using various computer systems.
Coordinate Grids:The plane coordinate grid systems 1983
(SPCS83) has been applied to all states.Software programs readily convert coordinates
based on one projection.
Transformation: If a GIS is tied to a specific coordinate grid and
orientation, the new data needs to be transformed to fit the working model.
Transformations can be made in:
- Grid reference,
- Scale
- Orientation.
The computer programs designed to translate from one grid reference to another, convert the scale, and rotate to appropriate orientation.
DATABASE MANAGEMENT: To organize the data so that the information about
entities and their attributes can be accessed by rapid computerized search and retrieval techniques.
Data collections can range in complexity.
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