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GIS and QGIS
Transcript of GIS and QGIS
CBMS Digitizing and Poverty Mapping
What is (and why) GIS?
Knowing where an event happened is critically important
Position of country boundaries
Location of hospitals
Routing delivery vehicles
Management of forest stands
Allocation of funds for sea defenses
What is GIS
“GIS is much more than a container of maps in digital form”
“GIS is a spatial decision support system”
“GIS is a mechanized inventory of geographically distributed features and facilities”
“GIS is a method for revealing patterns and processes in geographic information”
“GIS is a collection of computer hardware, software, and geographic data for capturing, managing, analyzing, and displaying all forms of geographically referenced information.”
What is GIS
information on the earth’s surface
knowledge about “what is where when
Global Positioning Systems (GPS)
a system of exploiting earth-orbiting satellites to provide location on the earth’s surface (in long-lat / cartesian or equiv.)
With a given precision (can 100 meter to sub-cm.)
GI Systems, Science & Studies
A little informal definition
A system of integrated computer-based tools for end-to-end processing (capture, storage, retrieval, analysis, display) of data using location on the earth’s surface for interrelation in support of operations management, decision making, and science.
Intuitive notion of GIS
A map with a database behind it
A virtual representation of the real world and its infrastructure.
A consistent “as-built” of the real world, natural and manmade
queried to support on-going operations
summarized to support strategic decision making and policy formulation
analyzed to support scientific inquiry
GIS Component Architecture
This work was carried out by the PEP-Asia CBMS International Network Coordinating Team with the financial support of the Government of Canada provided through the International Development Research Centre (IDRC) and the Government of United Kingdom through the Department for International Development (DFID).
This CBMS training material and related instruments are being shared for free use of local government units that are adopting the CBMS methodology under a memorandum of agreement (MOA) with the PEP-Asia CBMS International Network Coordinating Team.
GIS keeps track not only of events but also of where these events happen or exist
Geographic problems involve an aspect of location, either in the information used to solve them, or in the solutions themselves.
What S stands for?
- Technology (Systems)
- Concepts and theory (Science)
- Relevance to society (Study)
Remote Sensing (RS)
use of satellites or aircraft to capture information about the earth’s surface
Geographic Information Systems (GIS)
Software systems with capability for input, storage, manipulation/ analysis and output/display of geographic (spatial) information
Commercial or free/open-source
GPS and RS are usually serve of input data for a GIS.
set of integrated tools for spatial analysis
encompasses end-to-end processing of data
capture, storage, retrieval, analysis/modification, display
uses explicit location on earth’s surface to relate data
aimed at decision support, as well as on-going operations and scientific inquiry
THE GIS Data Model
The GIS Model: example
Here we have three layers or themes:
--topography (land elevation)
They can be related because precise geographic coordinates are recorded for each theme.
Layers are comprised of two data types
Spatial data which describes location (where)
Attribute data specifing what, how much,when
Layers may be represented in two ways:
in vector format as points and lines
in raster(or image) format as pixels
All geographic data has 4 properties:
projection, scale, accuracy and resolution
Geo-integration of Information
Data is organized by layers, coverages or themes (synonomous concepts), with each layer representing a common feature.
Layers are integrated using explicit location on the earth’s surface, thus geographic location is the organizing principal.
Spatial attribute and data
stored in a shape file, geodatabase or similar geographic file
Attribute (descriptive) data (what, how much, when)
specifies characteristics at that location, natural or human-created
stored in a data base table
GIS traditionally maintain spatial and attribute data separately, then “join” them for display or analysis
for example, in ArcView, the Attributes of … table is used to link a shapefile (spatial structure) with a data base table containing attribute information in order to display the attribute data spatially on a map
Spatial data representation
area is covered by grid with (usually) equal-sized, square cells
attributes are recorded by assigning each cell a single value based on the majority feature (attribute) in the cell, such as land use type.
Image data is a special case of raster data in which the “attribute” is a reflectance value from the geomagnetic spectrum
cells in image data often called pixels (picture elements)
The fundamental concept of vector GIS is that all geographic features in the real work can be represented either as:
points or dots (nodes): trees, poles, fire plugs, airports, cities
lines (arcs): streams, streets, sewers,
areas (polygons): land parcels, cities, counties, forest, rock type
Because representation depends on shape, ArcView refers to files containing vector data as shapefiles
Concept of Vector and Raster
Aspects of Spatial Representation
: the method by which the curved 3-D surface of the earth is represented by X,Y coordinates on a 2-D flat map/screen
distortion is inevitable
: the ratio of distance on a map to the equivalent distance on the ground
in theory GIS is scale independent but in practice there is an implicit range of scales for data output in any project
: how well does the database info match the real world
Positional: how close are features to their real world location?
Consistency: do feature characteristics in database match those in real world
is a road in the database a road in the real world?
Completeness: are all real world instances of features present in the database?
Are all roads included.
: the size of the smallest feature able to be recognized
for raster data, it is the pixel size
Higher specs—higher cost
Going Back: Why GIS?
Majority of local government activities estimated to be geographically based
plats, zoning, public works (streets, water supply, sewers), garbage collection, land ownership and valuation, public safety (fire and police)
Significant portion of state government has a geographical component
natural resource management highways and transportation (DPWH, DOTC, etc.)
Businesses use GIS for a very wide array of applications
retail site selection & customer analysis
logistics: vehicle tracking & routing
natural resource exploration (petroleum, etc.)
civil engineering and construction
Military and defense
Satellite imagery interpretation
Scientific research employs GIS
geography, geology, botany
anthropology, sociology, economics, political science
Provides a facility for storing a wide array of information generated from the conduct of a CBMS Census
One of its key features is that it can be used to generate desired information for presentation or reporting purposes in the form of digitized maps
It is an open source software, which can be used and distributed at NO cost
Quantum GIS (QGIS)
Poverty map on a Google Map
Community-based Monitoring System (CBMS) International Network
DLSU Angelo King Institute for Economic and Business Studies
10th Floor Angelo King International Center
Estrada corner Arellano Avenue, Malate, Manila, Philippines 1004
Tel. No.: (632) 5262067 or 2305100 loc. 2461
Fax Number: (632) 5262067
Facebook Page: http://facebook.com/CBMSPhilippines
Facebook Interactive Group: https://www.facebook.com/groups/CBMSNetwork/
Prepared by the CBMS Network Team
as of May 2017