ENGRG 59910 Introduction to GIS Michael Piasecki September 01, 2017 Lecture 02: Introduction to GIS and GIS Data Models
Outline today Part 1: What is GIS? GIS definitions GIS components GIS history Common GIS software Part 2: GIS Data Model Vector/Raster data model Common ESRI GIS file type ArcCatalog August 30, 2017 ENGRG 59910 Intro to GIS 2
What is GIS? Watch a short movie: What is GIS? (from http://www.esri.com/flashmedia/whatisgis.swf ) Search GIS definition in Google: Search phrase: define:gis August 30, 2017 ENGRG 59910 Intro to GIS 3
Definition 1: A GIS is a toolbox A powerful set of tools for storing and retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes. (Burrough, 1986) A system for capturing, storing, checking, manipulating, analyzing, and displaying data which are spatially referenced to the Earth (Department of Environment, 1987) An information technology which stores, analyses, and displays both spatial and non spatial data (Parker, 1988) August 30, 2017 ENGRG 59910 Intro to GIS 4
Definition 2: A GIS is an Information System (Database definitions) a System a group of connected entities and activities an Information System a set of procedures, executed on raw data, to produce information for decision making a Geographic Information System an Information System using geographically referenced data August 30, 2017 ENGRG 59910 Intro to GIS 5
Definition 3: GIS is an approach to science The science behind the technology Addresses the fundamental issues arising from use is the science needed to keep technology at the cutting edge Systematic study of geographic information and geographic information system technologies using scientific methods Analogy: GIScience is to GIS as statistics is to statistical software packages Reference: Michael F. Goodchild, and the project, NCGIA Core Curriculum in GIScience. 1997 August 30, 2017 ENGRG 59910 Intro to GIS 6
GIScience: Contributing Disciplines Geography Cartography Remote Sensing Photogrammetry Surveying Geodesy Statistics Operations research Computer Science Mathematics Information Science Management science August 30, 2017 ENGRG 59910 Intro to GIS 7
Scholarly Journals Emphasizing GIS Research International Journal of GIScience (formerly Intern l Journal of GISystems) Cartography and GIScience (formerly American Cartographer and Cartography and GISystems) Computers and Geosciences Computers, Environment and Urban Systems Photogrammetric Engineering and Remote Sensing Transactions in GISystems Geographical and Environmental Modeling Geographical Analysis GeoInformatica Annals of the Association of American Geographers Journal of Geographical Systems (successor to Geographical Systems) August 30, 2017 ENGRG 59910 Intro to GIS 8
Big Questions in GIScience http://www.ucgis.org/ dedicated to promotion of GIScience UCGIS > Priorities > Research > 2006 Research Agenda http://ucgis.org/publication/research priorities August 30, 2017 ENGRG 59910 Intro to GIS 9
Components of a GIS 1. Data 2. Hardware (computer system) 3. Software 4. Brainware: People/Procedures/Plan 5. Infrastructure: GIS operation environmental August 30, 2017 ENGRG 59910 Intro to GIS 10
Basic Elements of a GIS: Data Non Spatial Data Attributes or information that describes the spatial entity Spatial Data: geographically referenced data Latitude and longitude X and Y coordinates Street address Range and township Location shown on a map August 30, 2017 ENGRG 59910 Intro to GIS 11
GIS Data: Spatial is Special Geographic location is a key feature of 80 90% of all government data. (http://www.fgdc.gov/publications/homeland.html ) Experts estimate that as much as 80% of the cost associated with a GIS system is related to the development and maintenance of its spatial data Federal Agencies alone are spending $2.5 3.0 billion annually on collection and management of geospatial data (National Academy of Public Administration NAPA Geographic Information for the 21st Century, 2003/05/01) August 30, 2017 ENGRG 59910 Intro to GIS 12
Data Information Data numbers, text, symbols Sea surface temperature, soil type, population density Information differentiated from data implying some degree of selection, organization, and preparation for particular purpose, or data given some degree of interpretation Geographic Information (map, digital form) Information about places on Earth s surface Geographic versus spatial Geographic refers to Earth s surface and near surface Spatial refers to any space (more general) Knowledge about where something is Knowledge about what is at a given location Can be very detailed or very course Can be relatively static or change rapidly Can be very sparse or voluminous August 30, 2017 ENGRG 59910 Intro to GIS 13
Basic Elements of a GIS: Hardware Fast computer with a video card & video memory High resolution display Networking capabilities Optional: Digitizing tablet or large format scanner Flat bed scanner Large format plotter Printer (color or black & white) August 30, 2017 ENGRG 59910 Intro to GIS 14
Basic Elements of a GIS: Software Data management capabilities Analysis tools Display tools Information dissemination capabilities (import, export and map creation) Data entry features Editing capabilities August 30, 2017 ENGRG 59910 Intro to GIS 15
Basic Elements of a GIS: a Plan The recipe for implementing a GIS at the project or program level Clear description of the problem (frame the question) Understanding of the data needs to solve the problem (collect your data) Understanding of the GIS users and managers, desired outcomes: efficiency, increased knowledge Choose analysis methods Process the data Present the results August 30, 2017 ENGRG 59910 Intro to GIS 16
A typical GIS process: start to think about your final project now 1. Understanding basic geographic concepts Projections, datums, coordinate systems Reading maps 2. Formulating a game plan Planning the process 3. Acquiring data Data storage formats Data sources Data challenges 4. Database manipulation Attribute data Database management Computer database types 5. Analysis techniques Spatial analysis Models and modeling Cartographic Interpolation Dynamic modelling 6. Presenting the results Map creation and design August 30, 2017 ENGRG 59910 Intro to GIS 17
Evolution of GIS: From Stand alone to Web Services Mapping Troup Movements Manual Map overlays 1870 1950 1970ies 1980ies 1990ies 2000ies August 30, 2017 ENGRG 59910 Intro to GIS 18
GIS Web Service Chain Web Coverage Service Portrayal service assembles orthoimage from several imagery services Reprojection service the image from one coordinate system to another one Overlay service overlays the input image and the vector data and sends the overlay to the client Web Coverage Service Portrayal Service Reprojection Service To Client Web Coverage Service Vector Data Provider Service Vector data provider service returns a certain layer at the extent specified Overlay Service August 30, 2017 ENGRG 59910 Intro to GIS 19
Prevailing GIS Software ESRI: ArcGIS (desktop and server), ArcView and other products (http://www.esri.com) Quantum GIS, or QGIS, http://qgis.org/en/site/ (latest release: 2.18 Las Palmas) Intergraph: GeoMedia and MGE (http://www.intergraph.com) MapInfo Inc, MapInfo: http://www.mapinfo.com Autodesk: Autodesk Map, http://www.autodesk.com Baylor Unversity, Texas; University of Hannover, Germany, GRASS (Geographic Resources Analysis Support System): http://grass.itc.it/ (free) August 30, 2017 ENGRG 59910 Intro to GIS 20
Prevailing GIS Software (ctd) Manifold.net, Manifold System (http://www.manifold.net) Clark Labs, IDRSI, http://www.clarklabs.org PCI Geomatics, Geomatica, http://www.pcigeomatics.com Caliper Corporation, TransCAD, Maptitude, http://www.caliper.com Leica, ERDAS http://gis.leica geosystems.com/ ERMapper, ERMapper, http://www.ermapper.com SuperMap, SuperMap GIS, http://www.supermap.com (China) Free GIS software list: http://www.freegis.org Open source GIS: http://www.opensourcegis.org August 30, 2017 ENGRG 59910 Intro to GIS 21
Part 2: GIS Data Models Spatial Information is usually modeled in one of two ways: Vector Data Model Points Areas Lines Forest River Raster Data Model City Spatial data are represented by these three objects. (We will use the topological vector model often.) Space is divided into a regularly spaced grid; each cell is coded according to what is on the surface. August 30, 2017 ENGRG 59910 Intro to GIS 22
GIS Data Model Level Conceptual Model (object view or field view) GIS Data Model Vector or Raster GIS Data Structure (Shape, Coverage, Geodatabase) GIS File Structure August 30, 2017 ENGRG 59910 Intro to GIS 23
GIS Data Conceptual Model The strategy chosen depends on whether one takes the field view versus object view of reality Field view: geographic phenomena that vary continuously throughout space. Examples: elevation, precipitation, etc. Object view: an empty space littered with discrete objects. Examples: roads, buildings, utilities, etc. August 30, 2017 ENGRG 59910 Intro to GIS 24
GIS Data Model: Vector vs. Raster Real World point line polygon 0 1 2 3 4 5 6 7 8 9 0 R T 1 R T 2 H R 3 R 4 R R 5 R 6 R T T H 7 R T T 8 R 9 R Vector Representation Raster Representation August 30, 2017 ENGRG 59910 Intro to GIS 25
Data Modeling Processing After Bernhardsen 1999, p.39 August 30, 2017 ENGRG 59910 Intro to GIS 26
Multiple Representations August 30, 2017 ENGRG 59910 Intro to GIS 27
Spatial Data Spatial Data Raster Data Vector Data Attribute Data Metadata Non-topological Topological Simple Higher-level Data Vector or Raster? Type of operations Experience and viewers of GIS users Data availability Data quality and storage TIN Regions Dynamic Segmentation From: Intro. to GIS, Chang, 1997 August 30, 2017 ENGRG 59910 Intro to GIS 28
Vector Data Model point (node): 0 dimension single x,y coordinate pair zero area tree, oil well, label location line (arc): 1 dimension 2 1 y=2 x=1 Point: (1,2) two (or more) connected x,y coordinates 2 1 2 road, stream polygon : 2 dimensions four or more ordered and connected x,y coordinates first and last x,y pairs are the same encloses an area 1 2 1 1 2 Line: (1,2), (2,1) Polygon: (1,2), (2,1), (1,1), (1,2) census tracts, county, lake 1 2 August 30, 2017 ENGRG 59910 Intro to GIS 29
Two Common Vector Models Spaghetti model (non topological) Topological model C A B D August 30, 2017 ENGRG 59910 Intro to GIS 30
Spaghetti Vector Model Lines and points are entered and may be visible, but the program does not recognize the relationships between lines. Each line is represented as a separate feature with a start node and an end node, possibly vertices in between. Still exists during data entry and editing C You have to build topology somehow A B D August 30, 2017 ENGRG 59910 Intro to GIS 31
Why Topology Matters Getting data to line up, connect, intersect, move together Important for GIS operations and analyses Coordinate transformation Map projection Area calculations Queries In order to do this we use topology August 30, 2017 ENGRG 59910 Intro to GIS 32
Definition: Topology ESRI: The spatial relationships between connecting or adjacent coverage features (e.g., arcs, nodes, polygons, and points). For example, the topology of an arc includes its from and to nodes and its left and right polygons. Textbook: (Study of) shape invariant spatial properties of line or area features such as adjacency, contiguity, and connectivity, often recorded in a set of related tables (Bolstad, p. 32 33) Webster: (Study of) those properties of geometric forms that remain invariant under certain transformations, as bending, stretching, etc. (Webster s Encyclopedic Unabridged Dictionary) August 30, 2017 ENGRG 59910 Intro to GIS 33
Topological Vector Data Model The connections and relationships between objects are described independently of their coordinates August 30, 2017 ENGRG 59910 Intro to GIS 34
Topology vs. Coordinate (Continue) A topologically accurate map: relationships between subway stations are accurately shown. Actual locations and shapes of the tracks and tunnels are not accurate. August 30, 2017 ENGRG 59910 Intro to GIS 35
How to define GIS Topology Based on Point/Node: Where lines begin, end, or intersect Line/Link: Line segments between two nodes Polygon: composed of alternating links and nodes Unique identifiers are assigned to each link, node, and polygon Polygon Point/Node Line/Link August 30, 2017 ENGRG 59910 Intro to GIS 36
Define Topology Topology (relations) can be described in 3 tables. Polygon Topology Table: Links composing all the polygons. Node Topology Table: List of the links that meet at each node. Link (or line segment) Topology Table: List of the beginning and end nodes for each link; polygons to the right and left to the link. ( From node, To node, right poly, left poly August 30, 2017 ENGRG 59910 Intro to GIS 37
A Topology Example N3 L3 L2 C D A N2 L1 N4 L7 L4 N5 L5 N10 N6 B L6 N1 L9 N7 L8 D N8 Polygon Topology Table Polygon Links A B D L1,L2,L3,L4,L5,L6 L7,L8,L9,L6,L5,L4 L1,L2,L3,L7,L8,L9 Link Topology Table Link Start End Left Right L1 N1 N2 D A L2 N2 N3 D A L5 N5 N6 B A L9 N8 N1 D B Node Topology Table Node Links N1 N2 N3 L1,L6,L9 L1,L2 L2,L3 August 30, 2017 ENGRG 59910 Intro to GIS 38
Vector Data Creation input of the spatial data Digitizing/scan then vectorized Build topology input of the attribute data linking spatial and attribute data August 30, 2017 ENGRG 59910 Intro to GIS 39
Common Vector GIS Data Files Coverage (topological) Shape File (non topological) GeoDatabase (topological) MapInfo (topological) TIN (topological) CAD (non topology) August 30, 2017 ENGRG 59910 Intro to GIS 40
Raster Data Model The raster model represents reality (and feature geometry) through uniform, regular cells (pixels) Within each cell, the terrain is generalized to an areal unit in which attributes are constant Real World Overlay grid on the Real World Cells Raster representation August 30, 2017 ENGRG 59910 Intro to GIS 41
Raster Data Model The finer the grid size, the more precise the information about the real world is Real World Coarse detail Finer detail Cells are usually assigned the value of the object taking up the greatest part of the cell area Bolstad has a long discussion. August 30, 2017 ENGRG 59910 Intro to GIS 42
Attribute Data and Coor. System Each cell is identified by a row and column number. Attribute values are stored for each cell based on the majority feature (attribute) in the cell, such as land use type Location coordinates are calculated by adding or subtracting cell size x rows and columns to the known coordinates of the origin.. Generally, the midpoint of a cell is considered its location. BUT NOT ALWAYS (e.g. ENVI) (x,y) Rows 1 2 3 4... Columns 1 2 3 4 5 6... August 30, 2017 ENGRG 59910 Intro to GIS 43
Resolution In general, resolution can be defined as the minimum linear dimension of the smallest unit of geographic space for which data are recorded In the raster model the smallest units are generally rectangular (occasionally systems have used hexagons or triangles) ; these smallest units are known as cells, pixels High resolution refers to raster with small cell dimensions high resolution means lots of detail, lots of cells, large rasters, small cells August 30, 2017 ENGRG 59910 Intro to GIS 44
Raster Cell Size August 30, 2017 ENGRG 59910 Intro to GIS 45
Resolution and Scale August 30, 2017 ENGRG 59910 Intro to GIS 46
Raster as Thematic Layers Each layer can be treated separately But they can also be combined in a GIS because all objects are linked to a coordinate system. Spatial operations: Overlay Map algebra August 30, 2017 ENGRG 59910 Intro to GIS 47
Primary Uses for Raster Data Models describing continuous attributes of the real world. Elevation, soils, temperature, etc. Images (satellites, scanned maps, photographs). Output (e.g. Printers, plotters, monitors). Physical Variables Derived Variables, e.g. Distance from Points August 30, 2017 ENGRG 59910 Intro to GIS 48
Vector vs. Raster Data Model Continuous data (Raster) Simple data structure Large data volumes Easy overlay Rapid data collection Poor network analysis No topology stored (no relationships shown) High spatial variability Suitable for highly variable data Lower positional accuracy Determined by cell size Low geometric accuracy Better suited for imagery Discrete (Vector) Complex data structure Compact Data File Overlay is more difficult Slow data collection Possibility of Network analysis Efficient Topology Low spatial variability Good for homogeneous data Potentially excellent positional accuracy Given by (X,Y) coordinates High geometric accuracy Better suited for graphics August 30, 2017 ENGRG 59910 Intro to GIS 49
Data Conversion Data can be transformed from one of these data models to the other Vectorization Rasterization Some information is always lost when converting from one data format to the other. August 30, 2017 ENGRG 59910 Intro to GIS 50
Rasterization Vector Format Key points: Rasterization loses topological features No information about relationships Positional accuracy decreases Depends on cell size: Positional accuracy ~ ½ cell size Raster Format August 30, 2017 ENGRG 59910 Intro to GIS 51
Vectorization Raster Format Vector Format Key points: Feature boundaries become jagged in the vector representation Topology is created (relationships) August 30, 2017 ENGRG 59910 Intro to GIS 52
Data In ArcCatalog August 30, 2017 ENGRG 59910 Intro to GIS 53
Data File Display Differently Windows Explorer vs. ArcCatalog August 30, 2017 ENGRG 59910 Intro to GIS 54
ESRI GIS Data Files GeoDatabase Shapefile Coverage MXD file Pay attention to the icon shape and color Image August 30, 2017 ENGRG 59910 Intro to GIS 55
How shapefiles are stored Shapefiles: simple, non topological format, storing the geometric location and attribute information..shp the file that stores the feature geometry. Required..shx the file that stores the index of the feature geometry. Required..dbf the dbase file that stores the attribute information of features. Required..sbn and.sbx the files that store the spatial index of the features. Optional..fbn and.fbx the files that store the spatial index of the features for shapefiles that are read only. Optional..ain and.aih the files that store the attribute index of the active fields in a table or a theme's attribute table. Optional..prj the file that stores the coordinate system information. Optional..xml metadata for ArcGIS. Optional. Tech details: http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf August 30, 2017 ENGRG 59910 Intro to GIS 56
How coverage files are stored? Tech details: http://avce00.maptools.org/docs/v7_bin_cover.html August 30, 2017 ENGRG 59910 Intro to GIS 57
GeoDatabase Database data sets (RDBMS data sources), rather than file based data sets Supported by major RDBMS, such as DB2, SqlServer, Oracle, Microsoft Access (personal Geodatabase) August 30, 2017 ENGRG 59910 Intro to GIS 58
Personal Geodatabase Limited by 2G bytes before the ArcGIS version 9.1; Since ArcGIS 9.2, the Personal Geodatabase based on SqlServer Express does not have size limitation August 30, 2017 ENGRG 59910 Intro to GIS 59
MXD File Format ArcMap Map Document file It does not save your GIS data. Map document such as symbology, layer name saved only. Very important for your exercise: Relative Path vs. Full Path August 30, 2017 ENGRG 59910 Intro to GIS 60
Relative Path vs. Absolute Path August 30, 2017 ENGRG 59910 Intro to GIS 61
Absolute (full) and relative path An absolute, or full, path begins with a drive letter followed by a colon, such as D:. such as: G:\classes\FoundGIS\Data A relative path refers to a location that is relative to a current directory. August 30, 2017 ENGRG 59910 Intro to GIS 62
Why use relative vs. absolute path? Using absolute pathnames: You can move the document or toolbox anywhere on your computer and the data will be found when you reopen the document or tool. On most personal computers, the location of data is usually constant. That is, you typically don't move your data around much on your personal computer. In such cases, absolute pathnames are preferred. You can reference data on other disk drives. Using relative pathnames: (recommended in this class) When moving a map document or toolbox, the referenced data has to move as well. When delivering documents, toolboxes, and data to another user, relative pathnames should be used. Otherwise, the recipient's computer must have the same directory structure as yours. August 30, 2017 ENGRG 59910 Intro to GIS 63
Do not lose the big picture! Part 1: What is GIS? GIS definitions GIS components GIS history Common GIS software Part 2: GIS Data Model Vector and Raster Common ESRI GIS file type ArcCatalog August 30, 2017 ENGRG 59910 Intro to GIS 64