2 What is a Geographic Information System (GIS)? A GIS is a particular form of Information System applied to geographical data.An Information System is a set of processes, executed on raw data to produce information which will be useful when making decisions.A system is a group of connected entities and activities which interact for a common purpose.This discussion is derived from a seminar by Dr. David Waits
3 What is a Geographic Information System (GIS)? An information system has a full range of functions to:process observationsprocess measurementsprovide descriptionsexplain datamake forecastsmake decisions
4 What is a Geographic Information System (GIS)? In a geographic information system, information is characterized spatially.In a GIS the common purpose is decision making to manage:landresourcestransportationretailingOR any other spatially distributed activity
5 What is a Geographic Information System (GIS)? A GIS is an organized collection of computer hardware, software, geographic data, and personnel to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.A GIS integrates spatial and other kinds of information within a single system to provide a consistent framework for analyzing geographic (spatial) data.
6 What is a Geographic Information System (GIS)? A GIS makes connections between activities based on geographic proximity.The digital data structure can be conceptualized as a set of “floating electronic maps” with a common registration allowing the used to “look” down (drill down) and across the stack of maps.The spatial relationships can be summarized (data base inquiries)
7 What is a Geographic Information System (GIS)? The spatial relationships can be summarized (data base inquiries) or manipulated (analytical processing).Another definition of GIS - An internally referenced, automated, spatial information system for data mapping, management, and analysis
8 Convert Data to Digital Format GIS ProcessCapture DataRegister Map BaseInterpret DataStore Data in ComputerConvert Data to Digital FormatProcess DataDisplay Results
9 GIS System Spatial Data Base Attribute Data Base Cartographic Display SystemGeographic Analysis SystemMap Digitizing SystemImage Processing SystemStatistical Analysis SystemDatabase Management SystemImagesMapsStatistical ReportsStatistics Tabular DataGIS System
10 GIS - Map Stacking Geographic Information System pH Layer NDVI From Aerial ImageNitrogen AvailabilityEstimate fromAerial PhotopH LayerGeographicInformationSystemCourtesy of PPI
11 “Drilling Down” Through The Data Layers Courtesy of PPI
12 GIS Data Formats Raster Vector There are two formats used by GIS systems to store and retrieve geographical data:RasterVector
13 Raster Format Data are divided into cell, pixels, or elements Cells are organized in arraysEach cell has a single valueRow and Column Numbers are used to identify the location of the cell within the array.Perhaps the most common example of raster data is a digital image.
14 Vector FormatData are associated with points, lines, or boundaries enclosing areasPoints are located by coordinatesLines are described by a series of connecting vectors (line segments described by the coordinates of the start of the vector, its direction, and magnitude or length).Areas or polygons are described by a series of vectors enclosing the area.
15 Vector FormatAny number of factors or attributes can be associated with a point line or polygon.Data are stored in two files:a file containing location informationa file containing information on the attributesA third file contains information needed to link positional data with their attributes.
16 Vector and Raster Representation of Point Map Features GIS Vector FormatGIS Raster Format(X,Y) Coordinate in spaceCell Located in an Array
17 Vector and Raster Representation of Line Map Features GIS Vector FormatGIS Raster Format
18 Vector and Raster Representation of Area Map Features GIS Vector FormatGIS Raster Format
19 Vector and Raster Formats Most GIS software can display both vector and raster data.Raster formats are efficient when comparing information among arrays with the same cell size.Raster files are generally very large because each cell occupies a separate line of data.Vector formats are efficient when comparing information whose geographical dimensions are different.
20 Comparison of Raster and Vector Formats Raster formats are efficient when comparing information among arrays with the same cell size.Raster files are generally very large because each cell occupies a separate line of data, only one attribute can be assigned to each cell, and cell sizes are relatively small.Vector formats are efficient when comparing information whose geographical shapes and sizes are different.Vector files are much smaller because a relatively small number of vectors can precisely describe large areas and a many attributes can be ascribed to these areas.
21 Comparison of Raster and Vector Formats Raster representations are relatively coarse and impreciseVector representations of shapes can be very precise.Most GIS software can display both raster and vector data. Only a limited number of programs can analyze both types of data or make raster type analyses in vector formats.
22 Coordinate SystemsSpatial data are generally recorded as latitude and longitude, frequently as decimal degrees.Other systems commonly used are the Universal Transverse Mercatur - UTM and State Plane Coordinates. These systems are projections of the curved surface of the globe on to a plane surface.
23 Coordinate SystemsUTM, the preferred system, distance unit is the meter.The unit of the state plane system is the foot.There is generally a different coordinate system for each state in the state plane system.In the UTM system projections are made in zones of approximately 6 degrees of longitude.
24 Coordinate SystemsThere are two datums (reference planes) commonly used to make projections: North American Datum of 1927 (NAD27) and the World Geographic Reference System of 1984 (WGS84). The WGS84 datum can be used world wide. The default datum of many GPS receivers is the WGS84 datum.
26 UTM Specifications UTM position is specified by: Number of the ZoneNorth (or South) of the equatorEast of the western boundary of the zoneDistances are in metersCoordinates are referred to as “Northings” and “Eastings”N xxxxxx, E yyyyyy
27 Interpolation to Predict Missing Data Frequently, data are collect at discrete points located a significant distance apart or some of the data are missing.Interpolation is used to predict the values of the missing data.There a number of interpolation algorithms available in SST Toolbox and other software.
28 Interpolation Algorithms Nearest neighborLocal AveragingInverse distance to a powerRadial bias functionsShepard’s MethodKriging ANDSimple Contouring
29 What is the effect of the interpolation algorithm on the estimate of missing data? Selected Missing Data
30 Nearest Neighbor Value of the nearest measurement to the missing data. In the case of values at the same distance, the average of those valuesMissing DataNearest Neighbor
31 Local Average Average of all values within a predetermined distance. Missing DataAveraged Values
32 Inverse (Weighted) Distance Values are weighted by the inverse of their distance from the missing value. The weights can be raised to a power. The interpolated value is equal to the sum of the weighted values divided by the sum of the weights.Search Radius < 3 ftMissing Data
33 Inverse (Weighted) Distance Missing DataW = 1 W = W = 0.5 W = W = 0.354
34 Missing Values and Predicted Values Phosphorus at Efaw