GIS for NRM N.D.K. Dayawansa
GIS--What is it? Geographic/Geospatial Information information about places on the earth s surface knowledge about what is where when Geographic/geospatial: synonymous GIS--what s in the S? Systems: the technology Science: the concepts and theory Studies: the societal context
Citizens Inventory Geographic Knowledge The World Decision Support
Geographic Information Technologies Global Positioning Systems (GPS) a system of earth-orbiting satellites which can provide precise (100 meter to sub-cm.) location on the earth s surface (in lat/long coordinates or equiv.) Remote Sensing (RS) use of satellites or aircraft to capture information about the earth s surface Digital ortho images a key product (map accurate digital photos) Geographic Information Systems (GIS) Software systems with capability for input, storage, manipulation/analysis and output/display of geographic (spatial) information GPS and RS are sources of input data for a GIS.
Geographic Information Systems (GIS) Definitions The common ground between information processing and the many fields using spatial analysis techniques. (Tomlinson, 1972) A powerful set of tools for collecting, storing, retrieving, transforming, and displaying spatial data from the real world (Burroughs, 1986) A computerised database management system for the capture, storage, retrieval, analysis and display of spatial (locationally defined) data. (NCGIA, 1987) A decision support system involving the integration of spatially referenced data in a problem solving environment. (Cowen, 1988)
Geographic Information Systems Decision Define problem Output GIS Process Define GIS criteria GIS analysis Import or build datasets
Why Study GIS? Many government activities estimated to be geographically based zoning, public works (streets, water supply, sewers), garbage collection, land ownership and valuation, public safety (fire and police) natural resource management highways and transportation businesses use GIS for a very wide array of applications retail site selection & customer analysis logistics: vehicle tracking & routing natural resource exploration (petroleum, etc.) precision agriculture civil engineering and construction Military and defense Battlefield management Satellite imagery interpretation scientific research employs GIS geography, geology, botany anthropology, sociology, economics, political science Epidemiology, criminology
Examples of Applied GIS Urban Planning, Management & Policy Zoning, subdivision planning Land acquisition Economic development Code enforcement Housing renovation programs Emergency response Crime analysis Tax assessment Environmental Sciences Monitoring environmental risk Modeling stormwater runoff Management of watersheds, floodplains, wetlands, forests, aquifers Environmental Impact Analysis Hazardous or toxic facility siting Groundwater modeling and contamination tracking Political Science Redistricting Analysis of election results Predictive modeling Civil Engineering/Utility Locating underground facilities Designing alignment for freeways, transit Coordination of infrastructure maintenance Business Demographic Analysis Market Penetration/ Share Analysis Site Selection Education Administration Attendance Area Maintenance Enrollment Projections School Bus Routing Real Estate Neighborhood land prices Traffic Impact Analysis Determination of Highest and Best Use Health Care Epidemiology Needs Analysis Service Inventory
History of GIS Dr. John Snow and the 1854 Cholera outbreak in London's Broad Street region Source: John Snow Inc. www.jsi.com Dr John Snow is known as the father of modern epidemiology and the father of GIS He mapped the 1854 Cholera outbreak in London s Broad Street region. An outbreak of choledra in London in 1854 in the Soho district was typical of the time, and the deaths it caused are shown in the map. Source: UCLA http://www.ph.ucla.edu/epi/snow/snowmap1_1854_lge.htm Text source: Longley et al (2005)
Dr John Snow Dr. Snow noticed that the outbreak appeared to be centred on a public drinking water pump in Broad Street The pattern shown on the map would reflect the locations of people who drank the pump s water. Deaths had occurred in households that were located closer to other sources of water, but but their source of water is also the Broad Street pump. Source: http://blogs.esri.com/info/photos/geograp hy_matters/images/1440/secondarythumb. aspx Source: http://www.gisdevelopment.net/applicatio n/health/overview/images/image1.jpg Text source: Longley et al (2005
History of computers + GIS Early maps evidence of use of spatial data Post 1960s = computerized systems of cataloging and analyzing datasets, including geographic data, begin to be developed and used
History of computers + GIS Early 1970 s: Landsat satellite was launched which was capable of providing data on the earth surface Late 1970 s/early 1980 s: development of integrated software or computer code in publicly or commercially available packages ex. ERDAS (1978) by Leica-Geosystems ex. ArcInfo by ESRI (1981/82) ex. GRASS by US Army Corp (1982/1985) ex. MAPINFO (1986) ex. IDRISI (1987) by Clark Univserity, MA Source: bertalya.staff.gunadarma.ac.id
What is GIS? Some definitions of GIS focus on the hardware, software, data and analysis of components. However, no GIS exist in isolation from the organizational context, and there must always be people to plan, implement and operate the system as well as make decision based on the output. A Geographic Information System is not only about computers, software and electronic data. A GIS is an organised collection of : Hardware Software Network Data Procedures people! Source: Longley et al (2005) Geographic Information Systems and Science. 2 nd Edition. John Wiley and Sons Ltd.
Capabilities of GIS GIS will help to ask spatial questions that may be answered with one, two or more spatial data layers.
Example 1: Where is a given feature or set of features? "Where are forest stands greater than 100 years of age?" In the following dialog, I have specified a query asking for stands whose age in 1998 ("Age_1998") is greater than 100 years. The records that have matched the query criteria are displayed on the map in the default selection color of yellow.
Example 2: What features are at a given location? "What is the age of the forest near the 1050 Road?" The process is similar to the selection of stands within a certain age range, except first a particular road (the 1050 Road) is selected. Once the road is selected, we can use the spatial location of the selected road to make yet another selection against forest stands. The spatial selection will be all stands within 5 m of the selected road segment.
The following graphic shows a series of selected stands near the 1050 Road. The stands show up on the map in the selection color of yellow. To the lower left, the attribute table for the stands layer shows records for the selected stands. The age in 1998 is displayed in one of the fields. At the upper left is a selection of all the attributes of one particular stand.
Example 3: Where are areas that meet a given complex set of criteria? "What parts of the forest are located on > 30% slope, closer than 100 ft to a stream, and farther than 50 ft from a road?" The following graphic displays 10% slope classes. These were generated by a simple process performed on a digital elevation model.
These three datasets are merged; all properties of each dataset are stored in the final output. Each yellow polygon is coded for its status in each buffer type, as well as its slope class. Here is a display of a selection of polygons meeting our specified criteria:
Example 5: How can watershed analysis data be generated within a GIS? "What are the road and stream densities (mi / sq. mi) for the forest area? First, we eliminate roads and streams that are not within the forest area. This image shows streams and roads clipped to the administrative boundary of Pack Forest. Then we summarize the forest area (in square miles) and summarize the stream and road length (in miles). The quotient of (stream length / forest area) is the stream density, and (road length / forest area) is the road density: area length density forest 6.67 mi ^2 roads streams 54 mi 8.13 mi / mi^2 31 mi 4.62 mi / mi^2
Spatial data models two fundamental approaches: raster model vector model
Spatial Data Models Field-based models (e.g. RASTER) Continuous spatial phenomena For every point in space a value of the field can be determined Composite model Object-based models (e.g. VECTOR) Space is populated by well distinguishable, discrete, bounded objects, geo-relational model
Raster view of the world...
A raster dataset with cells half as large (e.g., 10 m on a side instead of 20 m on a side) may take up 4 times as much storage space, because it takes four 10 m cells to fit in the space of a single 20 m cell. The following image shows the difference in cell sizes, area, and number of cells for two configurations of the same total area:
Raster view of the world... Features Raster Tessellation Sampling
raster model The entity information is explicitly recorded for a basic data unit (cell, grid or pixel)
A few different types of raster data digital orthophoto digital elevation model (DEM)_
Vector model In a vector-based GIS data are handled as: Points X,Y coordinate pair + label Lines series of points Areas line(s) forming their boundary (series of polygons) line feature point feature area feature
vector model
Points: represent discrete point features each point location has a record in the table airports are point features each point is stored as a coordinate pair
Lines: represent linear features each road segment has a record in the table roads are linear features
Polygons: represent bounded areas each bounded polygon has a record in the table landforms and water are polygonal features
layers in a raster model Layer 1 Layer 2
layers in an vector-based model (1) Layer 2 Layer 1
layers in an vector-based model (2)
Comparison between raster and vector data models
Quadtree data structure In this, geographical area is decomposed into four quadrants and the decomposition continues until each quad represents a homogenous unit. The storage requirement of a quadree is much lower than that of a raster having the resolution of the smallest quad element
Quadtree data structure In this, geographical area is decomposed into four quadrants and the decomposition continues until each quad represents a homogenous unit. The storage requirement of a quadtree is much lower than that of a raster having the resolution of the smallest quad element
THE QUADTREE DATA STRUCTURE WORKS WITH: LEVELS QUADRANTS HOMOGENEOUS AREAS
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Quad trees advantages : - computation of standard region properties is easy - variable resolution and hence less storage requirement disadvantages : - translation invariant (two regions having same size and shape can produce different quadtrees. - cannot split into parts
Topology Topology is a branch of mathematics that deals with properties of space that remain invariant under certain transformations. Properties : 3 spatial relationships Containment: Polygons can be defined by set of lines enclose them Contiguity: Identification of polygons which touch each other or connect identify contiguous polygons (left or right) Connectivity: Identification of interconnected arcs, starting point & end point of network analysis
GIS topology Topology is a mathematics approach that defines unchangeable spatial relationships. When a map is stretched or distorted, some properties change, Distance Angles Relative proximities Some properties will not change Adjacencies Most other relationships, such as "is contained in", "crosses" Types of spatial objects - areas remain areas, lines remain lines, points remain points These unchanged properties are called topological properties.
Topological examples Network connectivity Polygon adjacency Topology poorly-defined Topology well-defined
Importance of topology Topology enables operations like connectivity and contiguity analysis. Searching a shortest path Finding a service area by using a road network Finding adjacent areas Topology enables spatial analysis without using a coordinate set, Apply spatial analysis using topological definitions alone Major difference from CAD or computer-aided cartography
Topology and GIS analysis Searching a shortest path Finding adjacent areas 1 2 3 2 2.5 2 2.5 The shortest path from the blue point to the yellow point is through the red point and then the orange point (2+1+2.5=5.5 map units). However, if the topology of the red point is not defined clearly, which means the two purple lines are consider as one and the two orange lines are considered as one, the resulting answer will be wrong (2+2+2=6 map units). 2 The overlapped two polygons have to be cut into three in order to clearly defined the spatial topology. Otherwise there will be difficulties finding an adjacent polygon of either.
Lines: fundamental spatial data model node vertex vertex node vertex vertex Lines start and end at nodes line #1 goes from node #2 to node #1 Vertices determine shape of line Nodes and vertices are stored as coordinate pairs
Polygons: fundamental spatial data model Polygon #2 is bounded by lines 1 & 2 Line 2 has polygon 1 on left and polygon 2 on right
Polygons: fundamental spatial data model complex data model, especially for larger data sets arc-node topology, used for ArcInfo data sets or defined by rules in the Geodatabase.
Buffers in GIS Why buffers are needed? For proximity analysis. Examples Point buffers Line Buffers Polygon Buffers
Buffers - Examples Point buffers Number of households around 5 km of the primary school. Number of wells that can be contaminated by a chemical factory due to a possible chemical leakage. Location of a water abstraction well that does not fall within 5km distance form a chemical factory. To assess whether asthma is more prevailing close to a incinerator. Line buffers Pollution sources located within the reservation areas of a small stream. Number of illegal constructions in the reservation area of the railway line from Point X to Y. Zones of noise pollution in major roads. To assess whether crimes are more prominent close to main roads Polygon buffers Banks located within 2 km distance from the central business district of a town. Number of small water bodies located within 5 km distance from the city limits.
This presentation has been produced with the help of the resources available in www