9/24/2015 R. Khosla Fall Semester 2015 1 Introduction to GIS Geographic Information Systems SOCR-377 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) GIS… Item on the internet’s comp.infosystems.gis FAQ list (FAQ = frequently asked questions) GIS… GIS: An introduction The real world
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9/24/2015
R. Khosla Fall Semester 2015 1
Introduction to GISGeographic Information
Systems
SOCR-377
Geographic InformationSystems
SOCR-377
What in the world is GIS?
GIS is simultaneously thetelescope, the microscope,the computer and the Xeroxmachine of regional analysisand synthesis of spatial data.
(Ron Abler, 1988)
GIS…
Item on the internet’s
comp.infosystems.gis FAQ list (FAQ = frequently asked questions)
GIS…
GIS: An introduction
The real world
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R. Khosla Fall Semester 2015 2
GIS Tools
• GIS is intended to be the means of improving everyday life
• It is important that information generated from data processingbe applied to guide the real world in the right direction
GIS…
Abstraction or
simplification
DataAnalysisResults
High
Medium
Low
50 lbs/ac
Take action
100 lbs/ac150 lbs/ac
Yield maps
The real world
•A traditional map can be both a presentationmedium and a storage medium
GIS…
STORAGE
+PRESENTATION
Traditional Maps
• wide variety of products can be created fromthe same basic data
GIS…
STORAGE
PRESENTATIONEnviron-mental
Roads Utilities Areas Farms
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GIS…Example of data set from Larimer County
Want to look at Cities and Towns in Larimer County
GIS…
40,665600 -104,996072 5347 12.1 Livestock
40,665595 -104,996072 5462 48.6 Cereals
40,665595 -104,996072 5311 7.6 Livestock
40,664756 -104,996646 5426 87.3 Cereals
40,664756 -104,998697 5401 0.3 Buildings
• For presentation purposes, the data in the table is translated into map symbols (objects)
• These symbols are then superimposed on existing map data
• 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
Buildings
Probable categories
Situated at
Represented by
Height
Governmental40.749668; -73.969170
Polygon
505 ft
Roads
Probable categories
Location
Represented by
Length
Avenue
A. 40.802198; -73.931245
B. 40.7222799; -73.988603
Polyline
125 blocs
ID Type Area X Y Height
1
2
3
Governmental
Commercial
Governmental
0.27
0.02
0.12
40.74
40.75
40.74
-73.96
-73.94
-73.91
505
370
478
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.
Final Product: Map Display
GIS…Data model
Database
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Vector dataIn vector data model, the objects are defined as points, lines or polygons.
GIS…
Point
Tree
Line Polygon
LakeFea
ture
sR
eal w
orld
•Examples of a Point feature (Tree)
•A line feature (River) •A polygon feature (Lake)
Vector data…
• Geographic information has dimension
• 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
GIS…
Longitude Latitude
-105.082771 40.572993
-105.082778 40.572989
-105.082778 40.572981
-105.082763 40.572978
-105.082761 40.572976
-105.082754 40.572970
-105.082748 40.572966
-105.082739 40.572977
Area consist of… Lines, which consist of…
Points, which consist of…
Coordinates
Geometric Objects.
Point: A zero dimensional object that specifies geometric location specified through a set of coordinates.
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.
Node: A zero dimensional object that is a topological function and may specify a geometric location.
GIS…
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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.
• 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.
• These data lie in a pile, just like Spaghetti.
• Several line segments are to be found in odd places in the data file.
MapTable
Line No. Coordinates
1
2
3
.
.
11
.
.
20
X, Y, Z
X, Y, Z
X, Y, Z
1
Y
X
3
20
GIS…Spaghetti data 20 nodes
Raster Data
• A two dimensional object (not bounded by lines)
• It is a method of storing, representing ordisplaying 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 gridis assigned an identifying value based on itscharacteristics
GIS…
GridCell
Generic Structure for a Grid
Raster Data
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 anidentifying value based on its characteristics
Columns
Row
s
GIS…
Grid Extent
Grid Resolution
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• 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
GIS…
Coded grid cells1. Buildings2. Trees3. Water bodies
• In raster format, data is stored in cells
• Each cell in a layer has a single attribute
GIS…
Soil layer in vector format
Soil layer in raster format
H
ML
GIS…
VectorRaster
Low resRaster
High res
• The higher the resolution, the smoother the edges
• The higher the resolution the larger the file
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R. Khosla Fall Semester 2015 10
• 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
GIS…
Forest type
Timber quality
Tree age
• 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
Cell No. Cell Type
11
12
13
14
15
16
17
.
.
76
77
78
.
.
81
82
0
0
1
0
0
2
0
.
.
3
3
0
.
.
2
2
Coded grid cells0. Unmapped1. Buildings2. Trees3. Water bodies
GIS…
GIS…
Point
Tree
Line
Polygon
Lake
Vector dataReal world Raster data
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GIS…
Some data benefit from being in raster format while other benefit from being in vector format
In a raster, every pixel contains information that needs to be stored
In a vector, only components of points, lines and polygons are stored
Converting raster to vector may result in loss of data
GIS…
• 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…
You are talking to a computer!
Where is the best part of my field?
• Select points where pH is above 8.5 and yieldis below 130 bu/A in field 31
GIS query
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GIS…
GIS query
“DryYield” < 130
GIS…
GIS query
GIS, is a tool which integrates spatial and non-spatial information over time