Introduction-Overview Why use a GIS? What can a GIS do? How does a GIS work? GIS definitions Spatial (coordinate) data model Relational (tabular) data model intro_gis.ppt 1
Why use a GIS? An extension of the paper map, but much more than a map, as you will see. GIS uses the analytical power of the computer to complete complex tasks. Computer's storage power to manage large data sets. Integration of many different types of data from many different sources. GIS maps a variety of different data to the same coordinate space (combination). Digital media are more stable than paper media, and easier to distribute via the net. Faster and easier update. Creation and use of "one-time" maps. Tailor-made maps. Elimination of some user bias. GIS brings new tools for thinking differently about geographic data. intro_gis.ppt 2
What can a GIS do? Generically Locate geographic features based on properties. Identify and analyze properties of geographic features based on location. Specifically Estimate economic effects of land-use regulation. Determine the optimal locations of new businesses. Generate optimal routing and scheduling delivery and repair services. Determine the ground area covered by a new cellular phone network. Delineate watershed boundaries for estimates of sedimentation effects. Predict vegetation types based on elevation, slope, and aspect. Predict landslide hazard for harvest units. Locate natural areas that need protection. Make colorful and interesting maps. intro_gis.ppt 3
The GIS Model: Examples roads longitude Here we have three layers or themes: --roads, --hydrology (water), --topography (land elevation) They can be related because precise geographic coordinates are recorded for each theme. hydrology longitude topography longitude Layers are comprised of two data types Spatial data which describes location (where) Attribute data specifying what, how much, and when Layers may be represented in two ways: 1. in vector format as points and lines 2. in raster(or image) format as pixels All geographic g data has 4 properties: p projection, scale, accuracy and resolution intro_gis.ppt 4
Examples of what a GIS can do Example 1: Where is a given feature or set of features? Where is Aurora Ave N? intro_gis.ppt 5
Examples of what a GIS can do Example 2: Where is a particular location? Where is the corner of Aurora Ave N & N 50 th St? intro_gis.ppt 6
Examples of what a GIS can do Example 3: What parcels will be affected by a road resurfacing project? Which parcels are within ½ mi of Aurora between N 35 th & N 50 th? intro_gis.ppt 7
Examples of what a GIS can do Example 4: Where are areas that meet a given complex set of criteria? What parts of the forest are located: closer than 100 ft to a stream, and farther than 50 ft from a road, on > 30% slope? intro_gis.ppt 8
Examples of GIS maps topographic mapping intro_gis.ppt 9
Examples of GIS maps orthophoto image maps intro_gis.ppt 10
Examples of GIS maps surface drapes & 3-D modeling intro_gis.ppt 11
Examples of GIS maps classified thematic mapping intro_gis.ppt 12
Examples of GIS maps research documentation intro_gis.ppt 13
How does GIS work? Combination i of coordinate data and tabular data each feature has a record intro_gis.ppt 14
GIS definitions "A system of hardware, software, and procedures designed to support the capture, management, manipulation, analysis, modeling and display of spatiallyreferenced data for solving complex planning and management problems." A working GIS integrates five key components: hardware, software, data, people, p and methods intro_gis.ppt 15
Spatial Data Model GIS are driven by spatial data - 2 basic spatial data models exist Vector 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, ArcGIS refers to files containing vector data as shapefiles Raster 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) intro_gis.ppt 16
Vector Data Model Characteristics of the vector data model: Features positioned accurately Shape of features represented correctly Features represented discretely (no fuzzy boundaries) Complex data structure (especially for polygons) point line polygon intro_gis.ppt 17
Vector Data Model Points: represent discrete point features intro_gis.ppt 18
Vector Data Model Lines: represent linear features intro_gis.ppt 19
Vector Data Model Lines: represent linear features Lines start and end at nodes line #1 goes from node #2 to node #1 Vertices determine shape of line _ intro_gis.ppt 20
Vector Data Model Polygons: represent bounded areas intro_gis.ppt 21
Vector Data Model Polygons: represent bounded areas Polygon #2 is bounded by lines 1 & 2 Line 2 has polygon 1 on left and polygon 2 on right intro_gis.ppt 22
Vector Data Model Polygons: represent bounded areas complex data model arc/node topology intro_gis.ppt 23
Vector Data Model Types (formats) of vector data available in ArcView ArcGIS shapefiles ArcInfo coverages and libraries CAD files (AutoCAD DWG, DXF; Microstation DGN) StreetMap files Spatial Database Engine (SDE) data ASCII point coordinate data intro_gis.ppt 24
Vector Data Model Shapefiles A vector data format Preferred in ArcGIS Draws fast Fully editable in ArcGIS Simple in structure Does not use arc-node topology Connected lines do not necessarily share a common node Adjacent polygons do not share common bounding arcs Data sets are either point or line or polygon intro_gis.ppt 25
Vector Data Model ArcInfo coverages A older commonly found format Data model more complex Draws more slowly in ArcGIS Coordinate data not editable in ArcGIS Can be used in both ArcGIS and ArcInfo Polymorphic Problematic file structure (more on this later in the term) intro_gis.ppt 26
Vector Data Model AutoCAD & Microstation CAD drawing data CAD data are very common (industry standard) DXF, DWG, and DGN formats supported in ArcGIS Coordinate data not editable in ArcGIS Frequently contain sloppy data No enforced topology rules Gaps in data Frequently contain little or no useful attribute data intro_gis.ppt 27
Vector Data Model ASCII coordinate data Easy to obtain from a variety of sources GPS Traverse Direct reading from maps OS, architecture, and application independent intro_gis.ppt 28
Raster Data Model Characteristics of the raster data model: Rectangular grid of square cells Shape of features generalized by cells Continuous o (surface) data represented easily Simple data structure intro_gis.ppt 29
Raster Data Model Raster data are good at representing continuous phenomena Wind speed Elevation, slope, aspect Chemical concentration Likelihood of existence of a certain species Electromagnetic reflectance (photographic or satellite imagery) intro_gis.ppt 30
Raster Data Model Raster spatial data model origin is set explicitly cell size is known cell references (row/column locations) are known cell values are referenced to row/column location values represent numerical phenomena or index codes for nonnumerical phenomena intro_gis.ppt 31
Raster Data Model A few different types of raster data digital orthophoto digital elevation model (DEM) intro_gis.ppt 32
Relational Database Model & Attribute Data Structures The where of GIS is determined by coordinate (map) data structures, but The what of GIS is determined by tabular (relational database) data structures Thus, tabular data are just as important as coordinate data intro_gis.ppt 33
Relational Database Model & Attribute Data Structures Attribute data are stored in database tables. Tables are composed of: fields and records intro_gis.ppt 34
Relational Database Model & Attribute Data Structures You may already be familiar with relational databases dbase rbase Access Excel (database functionality) Oracle, INFORMIX, INGRES, SQL Server INFO (in ArcInfo) intro_gis.ppt 35
Relational Database Model & Attribute Data Structures ArcGIS uses tabular data formats from dbase, ASCII text, and INFO files tables are stored on the drives as.dbf,.txt, or in INFO directories intro_gis.ppt 36
Relational Database Model & Attribute Data Structures Tables can be linked and joined ( related ) by use of common values in fields intro_gis.ppt 37
Relational Database Model & Attribute Data Structures Different types of attribute tables in ArcView Vector point attribute tables polygon attribute line attribute node attribute* text attribute* route & event tables* Raster value attribute * in ArcInfo coverage data only intro_gis.ppt 38