intro to gis. what is gis ? a computer system for - collecting, - storing, - manipulating, -...
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Intro to GIS
What is GIS ?A computer system for - collecting, - storing, - manipulating, - analyzing, - displaying, and - querying geographically related information.
Google Earth is an online GIS system
History of GIS1963-1977 innovationCanadian land inventory system, Harvard Graphics & S.A. Lab, US Census Bureau1981-1999ArcInfo, GPS, MapInfo, TIGER, NSDI, MapQuest2000-present exploitation>$7 billion industry, >1 million users
Demand for GIS professionalsIn the US in 2005500k using GIS as part of job; growing at 15% each yearJob market demand 75k/year50k US students/year take a GIS class4000 certified graduates/yearSource: ESRI
An example of GIS: composite of layers
In general GIS cover 3 componentsComputer systemHardwareComputer, plotter, printer, digitizerSoftware and appropriate proceduresSpatially referenced or geographic data People to carry out various management and analysis tasks
Geographic Data Geospatial data tells you where it is and attribute data tells you what it is. Metadata describes both geospatial and attribute data. In GIS, we call geographic data as GIS data or spatial data
1. Geospatial data
Traditional methodTo represent the geographic data is paper-based maps
Geology mapTopographic mapCity street map (we still use it a lot)...
GIS: a simplified view of the real worldPointsLinesAreasNetworksA series of interconnecting linesRoad networkRiver networkSewage networkSurfacesElevation surfaceTemperature surface
Discrete featuresContinuous features
PointsA point is a 0 dimensional object and has only the property of location (x,y)
Points can be used to Model features such as a well, building, power, pole, sample location ect.
Other name for a point are vertex, node
LinesA line is a one-dimensional object that has the property of lengthLines can be used to represent road, streams, faults, dikes, maker beds, boundary, contacts etc.Lines are also called an edge, link, chain, arcIn an ArcInfo coverage an arc starts with a node, has zero or more vertices, and ends with a nodeLine
Areas (Polygons)A polygon is a two-dimensional object with properties of area and perimeter
A polygon can represent a city, geologic formation, dike, lake, river, ect.
Other name for polygons face, zone
Topology neededA collection of numeric data which clearly describes adjacency, containment (coincidence), and connectivity between map features and which can be stored and manipulated by a computer.
A set of rules on how objects relate to each other
Major difference in file formats
Higher level objects have special topology rules
Two basic data models to represent these featuresRaster spatial data modelDefine space as an array of equally sized cells arranged in rows and columns. Each cell contains an attribute value and location coordinatesIndividual cells as building blocks for creating images of point, line, area, network and surfaceContinuous rasterNumeric values range smoothly from one location to another, for example, DEM, temperature, remote sensing images, etc.Discrete rasterRelative few possible values to repeat themselves in adjacent cells, for example, land use, soil types, etc.Vector spatial data modelUse x-, y- coordinates to represent point, line, area, network, surfacePoint as a single coordinate pair, line and polygon as ordered lists of vertices, while attributes are associated with each featuresUsually are discrete features
DIGITAL SPATIAL DATA RASTER VECTOR Real WorldSource: Defense Mapping School National Imagery and Mapping Agency
Raster and Vector Data Models Vector RepresentationX-AXIS500400300200100600500400300200100Y-AXISRiverHouse600 Trees TreesBBBBBBBBGGBKBBBGGGGG Raster Representation1234567891012345678910 Real WorldG G Source: Defense Mapping School National Imagery and Mapping Agency
Example: Discrete raster
Xie et al. 2005Example: continuous raster
RasterReal worldVectorHeywood et al. 2006
Effects of changing resolutionHeywood et al. 2006
Vector Advantages and DisadvantagesAdvantagesGood representation of realityCompact data structureTopology can be described in a networkAccurate graphicsDisadvantagesComplex data structuresSimulation may be difficultSome spatial analysis is difficult or impossible to perform
Raster Advantages and DisadvantagesAdvantagesSimple data structureEasy overlayVarious kinds of spatial analysisUniform size and shapeCheaper technologyDisadvantagesLarge amount of dataLess prettyProjection transformation is difficultDifferent scales between layers can be a nightmareMay lose information due to generalization
Grid PropertiesEach Grid Cell holds one value even if it is empty.A cell can hold an index standing for an attribute.Cell resolution is given as its size on the ground.Point and Lines move to the center of the cell.Minimum line width is one cell.Rasters are easy to read and write, and easy to draw on the screen.
2. Attribute dataAttribute data is about what of a spatial data and is a list or table of data arranged as rows and columnsRows are records (map features)Each row represents a map feature, which has a unique label ID or object IDColumns are fields (characteristics)Intersection of a column and a row shows the values of attributes, such as color, ownership, magnitude, classification,
3. metadataMeta is defined as a change or transformation. Data is described as the factual information used as a basis for reasoning. Put these two definitions together and metadata would literally mean "factual information used as a basis for reasoning which describes a change or transformation." In GIS, Metadata is data about the data. It consists of information that describes spatial data and is used to provide documentation for data products. Metadata is the who, what, when, where, why, and how about every facet of the spatial data. According to the Federal Geographic Data Committee (FGDC), metadata is data about the content, quality, condition, and other characteristics of data.
Why use and create metadataTo help organize and maintain an organization's spatial data - Employees may come and go but metadata can catalogue the changes and updates made to each spatial data set and how each employee implemented them To provide information to other organizations and clearinghouses to facilitate data sharing and transfer - It makes sense to share existing data sets rather than producing new ones if they are already available To document the history of a spatial data set - Metadata documents what changes have been made to each data set, such as changes in geographic projection, adding or deleting attributes, editing line intersections, or changing file formats. All of these could have an effect on data quality.
Metadata Should Include Data aboutDate of data collected.Date of coverage generated.Bounding coordinates.Processing steps.Software usedRMSE, etc.From where original data came.Who did processing.Projection coordinate SystemDatumUnitsSpatial scaleAttribute definitionsWho to contact for more informationSee an example of non-standard metadata (see)
Federal Geographic Data Committees (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM)The FGDC is developing the National Spatial Data Infrastructure (NSDI) in cooperation with organizations from State, local and tribal governments, the academic community, and the private sector. The NSDI encompasses policies, standards, and procedures for organizations to cooperatively produce and share geographic data. The objectives of the CSDGM are to provide a common set of terminology and definitions for the documentation of digital geospatial data.
CSDGM (FGDC-STD-001-1998) Metadata = Identification_InformationData_Quality_Information Spatial_Data_Organization_Information Spatial_Reference_Information Entity_and_Attribute_Information Distribution_Information Metadata_Reference_Information
Connect to http://www.fgdc.gov/metadata/csdgm/
4. GeodatabaseBefore geodatabase, in one GIS project, many GIS files (spatial data and nonspatial data) are stored separated. So for a large GIS project, the GIS files could be hundreds.Within a geodatabase, all GIS files (spatial data and nonspatial data) in a project can be stored in one geodatabase, using the relational database management system (RDMS)
Types of geodatabasespersonal enterprise
Personal GeodatabaseThe personal geodatabase is given a name of filename.mdb that is browsable and editable by the ArcGIS, and it can also be opened with Microsoft Access. It can be read by multiple people at the same time, but edited by only one person at a time. maximum size is 2 GB.
Multiuser GeodatabaseMultiuser (ArcSDE or enterprise) geodatabase are stored in IBM DB2, Informix, Oracle, or Microsoft SQL Server.
It can be edited through ArcSDE by many users at the same time, is suitable for large workgroups and enterprise GIS implementations. no limit of size. support raster data.
**GIS is a popular technology, but what exactly is it? What does it do? Basically, a geographic information system (GIS) is a computer-based tool for solving problems. A GIS integrates information in a way that helps us understand and find solutions to problems. Data about real-world objects is stored in a database and dynamically linked to an onscreen map, which displays the real-world objects. When the data in the database changes, the map updates to reflect t