# Review of GIS.pdf

## Transcript

2 What is GIS? What is “S” is GIS?...

2 What is GIS? What is “S” is GIS? Systems ▫ the technology TC 25 Science G eographic ▫ the concepts and Geographic Information Systems I nformation theory Studies Review of GIS Topics S ystems /Science/Studies ▫ the societal context Services 4 5 Definition of “Geographic” Definition of “Information” Data and information Defined as the knowledge that you get about Data only becomes useful, taking on value as of or relating to geography http://www.merriam-webster.com/ someone or something : facts or details about a information, within this context Geography: study of the lands, the features, the subject http://www.merriam-webster.com/ inhabitants, and the phenomena of Earth geographia meaning “earth description” DATA data = facts facts or information used usually to calculate, Information = facts with meaning Geographic: belonging to or characteristic of a analyze, or plan something http://www.merriam-webster.com/ particular region or location on the earth Information = data + context 7 8 9 Components of GIS What is “Geographic Information”? What is an “Information System”? DATA SOFTWARE Sometimes referred to as Spatial Information SYSTEM: a group of related parts that Information about places on the earth’s surface move or work together http://www.merriam-webster.com/ APPLICATION HARDWARE Knowledge about “what is where, when” S Links place/location, time, and attributes GIS INFORMATION SYSTEM: An association Example: of people, machines, data, and procedures “There are 2 students of TC 25 in UP Diliman at working together to collect, manage, and 9AM on Oct 12, 2022.” distribute information of importance to individuals or organizations PEOPLE Geographic Information System: intuitive descriptions Maps and GIS A map with a database GIS Operations behind it. Mapping is a key output of GIS but is not A virtual representation of In GIS, spatial data normally follows this the real world and its sequence of operations the whole story. infrastructure. GIS stores the spatial data that is used to make Data gathering and acquisition maps. Which is Pre-analysis processing queried to support on-going GIS analysis and manipulation GIS is an analysis tool operations summarized to support Map making and visualization strategic decision making and policy formulation analyzed to support scientific inquiry 13 4th Generation of GIS 7 Basic Questions GIS can deal with Beyond desktop GIS, beyond web GIS, beyond 4th Generation of GIS mobile GIS Can you map that? Cartographic Focus on ease of use, transparency and Where is what? Location widespread acceptance of location based systems Where has it changed? Temporal analysis for everyday life What relationship exists? Spatial analysis Ubiquitous (ever-present) GIS Where is it best? Spatial analysis What affects what? Systems modelling What if..? Simulation Geographic Information Technologies CURRENT TRENDS AND FUTURE OF GIS (3S) Global Navigation Satellite Systems (GNSS)/Global Positioning Systems (GPS) WebGIS and MobileGIS ▫ a system of earth-orbiting satellites which can provide Raster and Vector precise (10 meters to sub-cm.) location on the earth’s Realistic 3D Modeling surface (in lat/long coordinates or equiv.) Remote Sensing (RS) & Photogrammetry ▫ Virtual Environments ▫ use of satellites, aircrafts, or other platforms to capture ▫ Augmented Reality information about the earth’s surface ▫ Digital ortho images a key product (map accurate digital Indoor GIS photos) Geographic Information Systems (GIS) Big Data Analysis ▫ Software systems with capability for input, storage, manipulation/analysis and output/display of geographic (spatial) information 4 Levels of Modeling Conceptual MODEL LOGICAL MODEL (conceptualization/ abstraction) Can identify three conceptualisations of space: The two main types of GIS data models are: 1. Real World - in all its complex glory – Field-based – attributes can be thought of as Raster. Study area is divided into regular cells 2. Conceptual Model - your understanding of it varying continuously from place to place (e.g. (usually rectangular). Often used to model field data precipitation). Can be 2-D or 3-D (e.g. air Vector. Geometric primitives (i.e. points, lines, 3. Logical Model - possible computer realization polygons) are used to represent objects. pollution). (software independent) – Object-based – features can be thought of as 4. Physical Model - actual digital structure discrete entities or objects. Can be large or small, (software implementation) physical or counties, and con contain other objects. – Networks – object-based, but emphasis is on the interaction between objects along pathways. geospatial Data Models Raster and Vector Data Models Raster and Vector Data Models Raster ▫ Grid and cells Raster REAL WORLD ▫ For continuous data such as Satellite images elevation, slope, surfaces Scanned aerial Vector photographs, paper ▫ A series of x,y coordinates maps ▫ For discrete data represented Digital aerial Field-based model Object-based model as points, lines, polygons photographs Vector A Desktop GIS should be Land survey points able to handle both types GPS observation data Raster data model Vector data model of data effectively! Land parcels Road network Composition of Vector data Attributes for vector data Object Attributes Record non-spatial characteristics that describe Vector spatial entity any characteristic of an entity selected for representation Arranged in tables Stored in a flat-file format or database management system (DBMS) Reality Attribute table Attribute table a row is a column is equivalent to one equivalent to one entity attribute, or Raster each row relates descriptor, of that to a single object entity and a spatial data each object can model have multiple attributes that describe it (Review) Raster Data Model Raster Data Model Raster Data Model Treats geographic space as populated by one or more Best used to represent geographic features that are 1 #Rows & Columns (8 x 8) spatial phenomena, which vary continuously over continuous over a large area (eg. soil type, 2 space and having no obvious boundaries. vegetation, etc.) 3 Uses an array of rectangular cells/pixels/grids to Examples: 4 represent real-world objects. Elevation 5 Each cell is defined by a coordinate location and Air Temperature 6 an attribute that identifies the feature. Land ownership Grid Resolution 7 Similar features are assigned equal attribute values. Ice thickness (sides of a square) 8 The cell’s linear dimensions define the spatial Timber Volume or Biomass 1 2 3 4 5 6 7 8 resolution Population density e.g., 10 m resolution Getting Started with Geographic Information Systems, Clarke (2003) p. 91 (Review) Raster Data Model Raster Data Model Examples Data Input GIS Data Capture Processing GIS Data Collection Vector Primary Data Capture* DATABASE ▫ In-house creation of data (any survey, Coordinate Systems Raster Vector Raster photogrammetry, image analysis) ▫ Typically the most expensive part (~80% of project cost) Secondary Data Capture* ▫ From maps, reports, previous projects Maps, Plans ▫ DEMS from topographic map contours, scanned paper maps Surveying, Photogrammetry, Mapping * Capture connotes direct collection of data. COORDINATE SYSTEMS Y COORDINATE SYSTEMS COORDINATE SYSTEMS NORT Definitions H Definitions Definitions Two types: Latitude Prime Meridian Greenwich, London 60 E55 N Cartesian (by René Descartes) and Angular (spherical) Establish the reference for coordinates (locations) Equator Y 0 60 X Longitude Y 60⁰E 55⁰N latitude (φ): angular distance from equator; along Y axis (North-South) Geographical/spherical coordinate system Latitude/Longitude longitude (λ): angular distance from Cartesian/planar coordinate system Northing/Easting/Elevation standard meridian; along X axis (East-West) Northing and Easting - refer to Cartesian coordinates one-kilometer square on the ground. COORDINATE SYSTEMS COORDINATE SYSTEMS Prime Meridian Definitions DATUM Greenwich, London Definitions 0⁰00’00” EAST DATUM Horizontal Datums provides a frame of reference for Equator measuring locations on the surface of the 0⁰00’00” NORTH Earth chosen to align a spheroid to closely fit the Earth’s surface in a particular area COORDINATE SYSTEMS PHILIPPINE REFERENCE SYSTEMS Definitions Established by the Americans Established by the NAMRIA in 1992 DATUM during their Philippines occupation modified Luzon Datum Projections from The Philippines’ 0⁰00’00” GPS - led datum 52 UNIVERSAL TRANSVERSE MERCATOR (UTM) UNIVERSAL Transverse Mercator Philippine Transverse Mercator Philippines is at Zone 51 North Zone 51 North including Palawan Conformal projection (shapes are preserved) The Earth is divided into 60 zones, each 6° wide Problematic for areas at high latitudes and places that are located in two zones Commonly used for military applications and for mapping at a global or national coverage 121⁰E 54 PHILIPPINE TRANSVERSE MERCATOR ZONES Philippine Transverse Mercator Attribute Data in GIS Raster data ▫ Each cell can “own” only a single value ▫ Multi-attribute data will be represented 119 Attribute Data Operations by several raster 121 123 maps ▫ Each raster map will 3 3 3 3 3 1 1 1 1 1 As any projection has origin points, the origin points are particular to each projection. have an individual 3 3 3 3 3 1 1 1 1 1 The false easting is the x-coordinate value attribute table 3 3 3 3 3 1 1 1 1 1 assigned relative to this origin. 3 3 3 3 2 2 2 2 2 2 3 3 3 2 2 2 2 2 2 2 The false northing is the y-coordinate value 3 3 2 2 2 2 2 2 2 2 assigned relative to the same origin. 3 3 2 2 2 2 2 2 2 2 The true northing is reckoned from the equator. The true easting from Greenwich. 61 Attribute Data in GIS Vector data Field Calculation ▫ Multiple attributes may be contained in a single Use expressions or equations to input data in an Basic Table Operations attribute column table, if mapping units remain the same. Two ways to perform field calculation in QGIS: ▫ However, table may Field Calculation become too large and Table Join unwieldy, and difficult Table Querying to update as a result. Can be addressed by ID Area Site Owner Date Cost performing 1 Joins/Relates 2 3 4 5 6 Selection / Querying Table Join Two Types of Query for GIS Method of data retrieval Aspatial Query (Attribute Query) Joins Identify features that meet ▫ Questions about the attributes of ▫ Brings together 2 tables by using a common conditions features field or a primary key and a foreign key ▫ Example: “How many elementary schools are there?” Spatial Query Requires information about the location of a feature Example: “Where in Cagayan are elementary schools located?” Spatial Query (Selection by Aspatial: Table Queries Spatial Selection / Querying Location) Table queries a very common GIS Based on Spatial Relationships and aspatial operation Select a subset of records based Topology Intersect returns on values of specific attributes ▫ Adjacency – identifies features that share a any feature that Uses Set Algebra and Boolean boundary either fully or Operations partially overlaps the ▫ Intersect – identifies features that ‘touch’ source feature(s). ▫ Containment – identifies features that are ‘contained by’ (within) or ‘contain’ other features ▫ Distance – identifies features that are ‘within a set distance’ of a feature (proximity) Topological Relationships Topological Concepts ▪ Topological Relationships ▪ Interior, boundary, exterior ▫ invariant under elastic deformation (without tear, merge). Define Interior, boundary, ▫ Two countries which touch each other in a planar exterior on curves and points. Topology paper map will continue to do so in spherical U globe maps. Let A be an object in a “Universe” U. ▪ Topology is the study of topological Green is A interior ( Ao ) relationships Red is boundary of A (A) A Blue – (Green + Red) is A exterior ( A ) 9-Intersection Model of 9-Intersection Model of Topological Relationships Topological Relationships ▪ Topological Relationship between A and ▪ Intersection matrices for a few B can be specified using the nine topological operations intersection model ▪ Nine intersections Spatial Analysis ▫ Intersection between interior, boundary, exterior of A, B ▫ A and B are spatial objects in a two dimensional plane ▫ Can be arranged on a 3 x 3 matrix, thus the name 9- intersection Maps and GIS Characteristics of Spatial Data Spatial Analysis Mapping is a key output of GIS but is Objects with similar attributes usually are Besides the visual perception of the spatial located nearby spatially distribution of the phenomenon, it is very useful to not the whole story. ▫ Everything is related to everything else but translate the existing patterns into objective and nearby things are more related than distant measurable considerations (interpretation) ▫ GIS stores the spatial data that is used to things – First law of Geography Example: make maps in a spatial database ▫ This is called spatial autocorrelation ▫ Epidemiologists collect data about the occurrence of ▫ GIS is an analysis tool spatial Data values are not independent diseases. Does the distribution of cases of a disease form a pattern analyses as the add-on of GIS Most geographic locations are unique (spatial in space? heterogeneity) Is there any association with any source of pollution? ▫ Therefore, global parameters do not always Is there any evidence of contagion? accurately describe local values Did it vary with time? How can we characterize Spatial Spatial Analysis: successive levels of Analysis (what does it require)? sophistication GIS for Spatial Analysis and Modeling: 1. It requires knowledge of the problem and/or question 1. Spatial data manipulation: classic GIS capabilities to be answered ▫ Spatial queries & measurement, buffering, map layer Current leading commercial GIS software offers overlay decent analysis and modeling capabilities in 2. It requires knowledge about the data (how it was 2. Spatial data analysis: descriptive and exploratory areas such as: collected, organized, coded, etc.) ▫ Visualization through data manipulation and mapping ▫ Vector overlay 3. It requires knowledge of GIS capabilities John Snow’s maps of cholera in 1850s London ▫ Raster analysis 4. It requires knowledge of statistical techniques 3. Spatial statistical analysis: hypothesis testing ▫ Are data “to be expected” or are they “unexpected” ▫ Cartographic modeling 5. It requires envisioning the results of any operation and the combination of any operations relative to some statistical model, usually of a random ▫ Geostatistical estimation process ▫ Network analysis 6. It is not completely objective, in fact some argue that it 4. Spatial modeling: prediction is completely subjective ▫ Visualization of 2D and 2.5D data ▫ Constructing models (of processes) to predict 7. Many times there is more than one way to derive spatial outcomes (patterns) ▫ And 3D data (Source: Maguire, 2005; Lo & Yeung, 2002) information that answers a question ▫ What if analyses GIS for Spatial Analysis and Modeling: GIS for Spatial Analysis and Modeling: GIS for Spatial Analysis and Modeling: Current leading commercial GIS software offers Current leading commercial GIS software offers Current leading commercial GIS software offers decent analysis and modeling capabilities in decent analysis and modeling capabilities in decent analysis and modeling capabilities in areas such as: areas such as: areas such as: ▫ Vector overlay ▫ Vector overlay ▫ Vector overlay ▫ Raster analysis ▫ Raster analysis ▫ Raster analysis ▫ Cartographic modeling ▫ Cartographic modeling ▫ Cartographic modeling ▫ Geostatistical estimation ▫ Geostatistical estimation ▫ Geostatistical estimation ▫ Network analysis ▫ Network analysis ▫ Network analysis ▫ Visualization of 2D and 2.5D data ▫ Visualization of 2D and 2.5D data ▫ Visualization of 2D and 2.5D data ▫ And 3D data ▫ And 3D data ▫ And 3D data (Source: Maguire, 2005; Lo & Yeung, 2002) (Source: Maguire, 2005; Lo & Yeung, 2002) (Source: Maguire, 2005; Lo & Yeung, 2002) GIS for Spatial Analysis and Modeling: GIS for Spatial Analysis and Modeling: GIS for Spatial Analysis and Modeling: Current leading commercial GIS software offers Current leading commercial GIS software offers Current leading commercial GIS software offers decent analysis and modeling capabilities in decent analysis and modeling capabilities in decent analysis and modeling capabilities in areas such as: areas such as: areas such as: ▫ Vector overlay ▫ Vector overlay ▫ Vector overlay ▫ Raster analysis ▫ Raster analysis ▫ Raster analysis ▫ Cartographic modeling ▫ Cartographic modeling ▫ Cartographic modeling ▫ Geostatistical estimation ▫ Geostatistical estimation ▫ Geostatistical estimation ▫ Network analysis ▫ Network analysis ▫ Network analysis ▫ Visualization of 2D and 2.5D data ▫ Visualization of 2D and 2.5D data ▫ Visualization of 2D and 2.5D data ▫ And 3D data ▫ And 3D data ▫ 3D data (Source: Maguire, 2005; Lo & Yeung, 2002) (Source: Maguire, 2005; Lo & Yeung, 2002) (Source: Maguire, 2005; Lo & Yeung, 2002)