INTRODUCTION TO GEOGRAPHIC INFORMATION SYSTEMS

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INTRODUCTION TO GEOGRAPHIC INFORMATION SYSTEMS

• Robert A. Rose
• Geographic Information Systems Instructor
• rarose_at_fas.harvard.edu

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GOALS

• Answer the question What is a GIS?
• Learn some of the basic terminology used in a GIS
• Become familiar with the general operations and
  applications of a GIS
• See some of the analyses performed in a GIS

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What is a GIS?

• More than just an electronic map maker
• More than a digital database
• More than just a software package

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What is a GIS?

• A GIS is a computer system capable of assembling,
  storing, manipulating, and displaying
  geographically referenced information, i.e. data
  identified according to their locations.
• A GIS also includes operating personnel and the
  data that go into the system.

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Components of a GIS
GIS
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Geographic Information

• Location

• Attributes

• Spatial Relationships

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Geographic Objects

• So the question arises How do we represent an
  object in space with a computer?
• An object is any geographically referenced entity
• Lake, river, road, country, sampling site, etc.

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Geographic Information System

• Representations of geographic reality
• geometry
• location
• Linking attribute data to those objects
• Building spatial relationships between objects

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Representations of Geographic Reality The Data
Model Approach
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Data Models

• A data model is the method used to represent real
  world objects in a computer
• Two common methods are used
• Vector data model
• Raster data model

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Vector Data Model

• Abstract spatial features
• Point
• Line
• Area (polygon)
• Record coordinates
• Good for representing clearly defined objects
• Spatial relationships can be defined

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Point
Line
Area or Polygon
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ARC Example View 3 types of data in ARC
Catalog Data models example
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Raster Data Model

• Regular grid of cells
• Each cell represents an area on the ground
• Spatial resolution
• Value assigned to cell represents attribute
• Reflectance
• Land cover
• Elevation
• Satellite images
• DEMs
• Good for representing continuously changing
  attributes

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ARC Exercise Examine raster data in ARC Catalog
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Location

• Absolute locations
• Described by coordinate system
• geographic
• projected
• Relative locations
• Described through a relationship between objects.

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Geographic Coordinate Systems

• Reference system for curved surface of earth
• Network of intersecting lines
• graticule
• longitude
• latitude

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Projected Coordinate System

• Reference system for features on a flat
  (projected) surface
• Cartesian coordinate system with designated
  origin
• Many different projected coordinate systems
• UTM
• State Plane Coordinates

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Map Projections

• Projection of round earth onto flat surface

• Common
• Transverse Mercator
• Robinson
• Albers

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ARC Exercise projections example
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Linking Attributes to Geographic Representation
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Attributes

• Non-spatial data associated with objects
• Information about the objects in our GIS
• Land cover
• Stream name
• Flow rate
• Land owner
• Address
• Stored in tables that are linked with objects
• Polygon Attribute Table, Arc Attribute Table,
  Point Attribute Table

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ARC Exercise using ARC Catalog - examine
attributes associated with point, arc and
polygon files - look at tables
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GIS as a Database

• Links attribute data to spatial data
• Spatially relates different objects
• Topology
• Allows for spatial and attribute data queries and
  analysis

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ARC Exercise look at links between record in PAT
and layer tables map
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Spatial Relationships between Geographic
Representations
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Spatial Relationships

• Geometric characteristics of individual objects
• Length, area, perimeter, shape
• Spatial relationships between 2 or more objects
• Distance, direction, topology
• Spatial distribution of objects
• How objects are distributed in space

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Topology

• Topology is defined as the spatial relationships
  between adjacent or neighboring features.

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Fundamental GIS Operations
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Fundamental GIS Operations

• Capture
• Store
• Edit
• Analysis
• Display
• Output

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Capturing Data

• Databases
• GPS
• Remote Sensing
• Digitizing
• Existing Coverages
• Scanning
• Others

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WEB data sources
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Data Storage

• Through database management system
• Links attribute to spatial information

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Data Editing

• Updating or correcting features
• shapes and attributes
• Typically done in ARC Map

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GIS Analysis

• Visualizing and combining geographic data to
  derive new information
• Queries
• attribute, location
• Geoprocessing
• Analysis of spatial relationships between objects
  in a layer or objects in multiple layers
• create new data sets

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Data Query

• Queries are used to pull information out of a GIS
• You can think of a query as a question posed to
  the GIS
• Replies with both spatial and attribute
  information

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Geoprocessing

• Any GIS operation that creates new data
• Simple
• Copy one data set and paste it somewhere else
• Advanced
• Multiple operations on multiple data sets to
  create new, unique features

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Advanced Geoprocessing

• Data extraction
• creating a subset of features from one data set
  based on the geographic extent of another

• Overlays
• combination of two or more data sets to create
  new data set

• Proximity
• finding areas that are near features

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Fire Assessment

• You will assess the damage to riparian habitat,
  which is prone to erosion, along the creeks. You
  are going to map the area within 200 meters of
  the creeks so that the amount of erosion control
  materials that will be needed for remediation can
  be calculated.
• In addition to riparian habitat, the fire also
  burned a broader wilderness area. You will find
  the amount of forest that burned on each day.

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Display/Output

• A GIS provides the tools to display layers that
  allow the user to visually analyzed geographic
  relationships
• ArcMap
• Overlay different themes
• Design a map using data layers and output in
  multiple formats

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Map Design Example
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Campus Resources

• ARC GIS _at_ GSD
• http//www.gsd.harvard.edu/geo/manual/
• http//www.gsd.harvard.edu/geo/manual/arcgis_howto
  .htminstall
• http//www.gsd.harvard.edu/pbcote/courses/gsd6322/
  
• ESRI Virtual Campus
• http//www.gsd.harvard.edu/geo3/apps/evc.htm
• Harvard Map Collection
• GIS Support
• Harvard Geospatial Library

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Summary

• A GIS combines
• Spatial and attribute database
• Processing tools
• Graphic Capabilities
• Users
• Create a system of advanced spatial analysis for
  multiple uses
• Questions?