Introduction to GIS Geographic Information Systems SOCR-377 What in the world is GIS? GIS is simultaneously the telescope, the microscope, the computer and the Xerox machine of regional analysis and synthesis of spatial data (Ron Abler, 1988) Item on the internet s compinfosystemsgis FAQ list (FAQ = frequently asked questions) GIS: An introduction The real world R Khosla Fall Semester 2015 1
The real world GIS Tools Abstraction or simplification Take action 50 lbs/ac 100 lbs/ac 150 lbs/ac Results Medium Analysis Data Low High GIS is intended to be the means of improving everyday life It is important that information generated from data processing be applied to guide the real world in the right direction Yield maps Traditional Maps STORAGE + PRESENTATION A traditional map can be both a presentation medium and a storage medium STORAGE Environmental Roads Utilities Areas Farms PRESENTATION wide variety of products can be created from the same basic data R Khosla Fall Semester 2015 2
Example of data set from Larimer County Want to look at Cities and Towns in Larimer County Table Information Map symbol Lat Lon Alt Area Category 40,665600-104,996072 5347 121 Livestock 40,665595-104,996072 5462 486 Cereals 40,665595-104,996072 5311 76 Livestock 40,664756-104,996646 5426 873 Cereals 40,664756-104,998697 5401 03 Buildings Base map For presentation purposes, the data in the table is translated into map symbols (objects) These symbols are then superimposed on existing map data Maps: http://lasdepauledu/geography/programs/certificateingis/indexasp R Khosla Fall Semester 2015 3
Strategic Level Decision making Analysis and refining of data Real world By use of GIS a simplified world can be brought into the computer Different techniques can be applied to analyze and simplify the data, and foundation is laid for the decision making pyramid Today, GIS are in the process of filling the upper half of pyramid GIS Chain Expertise Structured data Organization Hardware / Software Farmer/ Consultant/ Agronomist Farm Operations Weather Marketing/Output Purchases By year By field By Farm By Operation MapInfo ArcInfo FarmGPS Farm HMS A GIS system cannot be bought off the shelf The system has to be built up within an organization When planning to introduce GIS, it is important that equal attention be given to all four links in the GIS chain Customers Streets Parcels Lat: 4052 o Lon: -10524 o Elevation Land usage Real world One can visualize the data stored as theme layers in the computer, with each layer linked to a common georeferencing system R Khosla Fall Semester 2015 4
Real World Real World Model Entity: Farm, Forest, City -Type Crop Farm, Dairy Farm, Livestock Farm, Poultry Farm - Attributes Large, Small, Corn, Wheat, Soybean - Relationship Land, Equipment, Labor, water, aquifer, ditch To bring real world into GIS, one has to make use of simplified models of real world Real World Real World Model Data Model Database Maps/Reports Entity: -Type - Attributes - Relationship Object: Object: -Type -Type - Attributes - Attributes - Relationship - Relationship - Geometry: point, line, area - Geometry - Quality: quality parameters -Quality Symbol, Line, Text To bring real world into GIS, one has to make use of simplified models of real world Uniform phenomena can be classified and described in the real world model Real world model is converted into data model by applying elements of geometry and quality The data model is transferred to a data base (tables/spreadsheets) that can handle digital data From which data can be presented/displayed Real World Real World Model Data model Buildings Probable categories Situated at Represented by Height Governmental 40749668; -73969170 Polygon 505 ft Roads Probable categories Location Represented by Length Avenue A 40802198; - 73931245 B 407222799; - 73988603 Polyline 125 blocs Database ID Type Area X Y Height 1 Governmental 027 4074-7396 505 2 Commercial 002 4075-7394 370 3 Governmental 012 4074-7391 478 Final Product: Map Display Modeling process: The transformation of real world into GIS products is achieved by means of simplification and models in the form of maps and reports R Khosla Fall Semester 2015 5
Vector data In vector data model, the objects are defined as points, lines or polygons Examples of a Point feature (Tree) A line feature (River) A polygon feature (Lake) Features Point Tree Line Polygon Lake Real world Vector data Area consist of Lines, which Points, which Geographic information consist has dimension of consist of Longitude Latitude -105082771 40572993-105082778 40572989-105082778 40572981-105082763 40572978-105082761 40572976-105082754 40572970-105082748 40572966-105082739 40572977 Coordinates Areas are 2-dimensional (2D) which consists of lines, which are 1-dimensional, and consists of points, which are zero-dimensional and consist of a coordinate pair Entire world of vector data consist of POINTS, LINES AND POLYGONS Point: A zero dimensional object that specifies geometric location specified through a set of coordinates Node: A zero dimensional object that is a topological function and may specify a geometric location Line Segment: A one directional segment that is a direct line between two end points Link: A one directional object that is a direct connection between two nodes Directed Link: A link between two nodes with one direction specified String: A sequence of line segments Geometric Objects R Khosla Fall Semester 2015 6
Chain: A directed sequence of nonintersecting line segments with nodes at each end Arc: A locus of points that forms a curve that is defined by mathematical function Also defined as a string or a chain Geometric Objects ID Longitude Latitude Y (Latitude) 1-10508277 4057299 14 2-10508278 4057299 3-10508278 4057298 4-10508276 4057298 5-10508276 4057298 6-10508275 4057297 7-10508275 4057297 8-10508274 4057298 9-10508277 4057299 10-10508278 4057299 11-10508278 4057298 12-10508276 4057298 13-10508276 4057298 14-10508275 4057297 Y = = 023X mx+b 3 + 071X 2 49X 113 X (Longitude) Y 10 100 1 X Each object is assigned attributes and coordinates Geometry ID Thematic Codes Attributes Coordinates Point Line Area 1 10 100 1000 7000 5000 A C C B D E 4, 3 (Single Point) 2,1 11, 5 5, 9 (String) 14, 10 12, 14 14, 10 (Closed Polygon) The number of coordinates for lines and polygons will vary considerably, depending on the length of the line and the circumference of the polygon This may make it inappropriate to store attributes and geometry together and is one of the reasons that many systems store them separately R Khosla Fall Semester 2015 7
Y Spaghetti data 1 Map 3 20 nodes Table Line No Coordinates 1 X, Y, Z 2 3 11 X, Y, Z 20 X, Y, Z X Spaghetti data is a term often used to describe digital map data with crossing lines, loose ends, double digitalization of common boundaries between adjacent polygons and so on 20 These data lie in a pile, just like Spaghetti Several line segments are to be found in odd places in the data file Raster Data A two dimensional object (not bounded by lines) It is a method of storing, representing or displaying spatial data in digital form It consists of cell data (not necessarily square) arranged in a regular grid pattern in which each unit (pixel or cell) within the grid is assigned an identifying value based on its characteristics Raster Data Generic Structure for a Grid Grid Cell Grid Extent Rows Grid Resolution Columns Raster Cell/Pixel: A two dimensional object (not bounded area) It is a method of storing, representing or displaying spatial data in digital form It consists of cell data (not necessarily square) arranged in a regular grid pattern in which each unit (pixel or cell) within the grid is assigned an identifying value based on its characteristics R Khosla Fall Semester 2015 8
Coded grid cells 1 Buildings 2 Trees 3 Water bodies Raster data can be visualized as a grid lying over the terrain Each grid cell has a code stored in the database describing the terrain within the particular cell L H M Soil layer in vector format Soil layer in raster format In raster format, data is stored in cells Each cell in a layer has a single attribute Vector Raster Low res Raster High res The higher the resolution, the smoother the edges The higher the resolution the larger the file R Khosla Fall Semester 2015 9
Forest type Timber quality Tree age Only one attribute value may be assigned to each cell Objects that have several attributes are therefore represented with a number of raster layers, one for each attribute Coded grid cells 0 Unmapped 1 Buildings 2 Trees 3 Water bodies Cell No 11 12 13 14 15 16 17 76 77 78 81 82 Cell Type A line and the column number define the cell s position in the raster data The raster data are then stored in the table giving the number and attribute value of each cell 0 0 1 0 0 2 0 3 3 0 2 2 Real world Vector data Point Raster data Tree Line Polygon Lake R Khosla Fall Semester 2015 10
Some data benefit from being in raster format while other benefit from being in vector format Converting raster to vector may result in loss of data In a vector, only components of points, lines and polygons are stored In a raster, every pixel contains information that needs to be stored A GIS can display and analyze data as multiple layers of the same field Each layer may represent one of the following: field boundaries, soil ph, drainage tiles, yield values, etc We could run queries and data analysis to make a better on-farm decision GIS query Where is the best part of my field? Select points where ph is above 85 and yield is below 130 bu/a in field 31 You are talking to a computer! R Khosla Fall Semester 2015 11
GIS query DryYield < 130 GIS query So, what is GIS? GIS, is a tool which integrates spatial and non-spatial information over time to make better decisions R Khosla Fall Semester 2015 12