GIS 101: Introduction to Geographic Information Systems

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GIS 101 Introduction to Geographic Information
Systems

• Week 6
• GIS Databases and Effective Usage
• Mid-Term Review

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GIS Databases and Effective Usage

• GIS data can be stored in many ways.
• Simple Files on the desktop- Desktop User
• Large complex databases- Server-Clients

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GIS Databases and Effective Usage

• Understanding the data storage method for the
  file type and/or software which you are using is
  critical.
• Each method has advantages and disadvantages.

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GIS Databases and Effective Usage

• GIS users should learn to be proficient with
  windows explorer as well as understanding files,
  folders, and directories.
• Movement of GIS data layers within a system will
  depend on that ability.

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GIS Databases and Effective Usage

• ESRI data models
• ArcView Shapefiles
• Arc/Info Coverages
• ArcGIS Geodatabase Layers
• Use of Spatial Database Engine (SDE)

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Mid-Term Review

• There will be all types of questions
• Multiple Guess
• Fill-in the blanks
• True or False
• Short Answer
• may include drawing or diagramming

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What is a GIS?

• A Geographic Information System (GIS) is a
  computer-based tool for displaying and analyzing
  things (man-made or natural) that exist and
  events that happen on earth. GIS technology can
  be applied at the scale of the entire globe, or a
  single property.
• GIS technology integrates common database
  operations such as query and statistical analysis
  with the unique visualization and geographic
  analysis benefits offered by maps

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What is a GIS?

• ESRI a GIS is made up of Data, Software,
  Hardware, and People.
• Some now add a fifth element Methods.

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Cartography

• The art, science, and craft of mapmaking.
• Cartography is the science that deals with the
  construction, use, and principles behind maps.

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Cartography Map Elements

• MAP itself to be most prominent feature
• Legend - Explaining the map features
• Title Subtitles - Descriptive Clear
• Neatlines - Separating map elements
• Scale bar - Describing the scale
• North Arrow - Indicating direction

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Map Projections

• Geoid- a figure that adjusts the best ellipsoid
  and the variation of gravity locally. It is the
  most accurate, and is used more in geodesy than
  GIS and cartography.
• Ellipsoid- An ellipsoid is an ellipse rotated in
  three dimensions about its shorter axis.
• Sphere- The sphere of the earth is about 40
  million meters in circumference. (24000 Miles)

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Map Scale and Projections

• Map scale is based on the representative
  fraction, the ratio of a distance on the map to
  the same distance on the ground.
• To compare or edge-match maps in a GIS, both maps
  MUST be at the same scale and have the same
  extent.
• The metric system is far easier to use for GIS
  work. But going between imperial and metric
  measurements can be a juggling act.

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Map Scale and Projections

• Geographic coordinates are the earth's latitude
  and longitude system ranging from 90 degrees
  south to 90 degrees north in latitude 180 degrees
  west to 180 degrees east in longitude.
• A line with a constant latitude running east to
  west is called a parallel.
• A line with constant longitude running from the
  north pole to the south pole is called a meridian.

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Map Scale and Projections

• All map projections representing all or part of
  the Earths surface as a flat map, create
  distortions in distance, area, shape, or
  direction.

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Map Scale and Projections

• A projection that preserves the shape of features
  across the map is conformal.
• A projection that preserves the area of a feature
  across the map is equal area or equivalent.
• No flat map can be both equivalent and conformal.
  Most fall between two as compromises.

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Coordinate Systems

• A coordinate system is a standardized method for
  assigning code locations so that locations can be
  found using the codes alone.
• Standardized coordinate systems use absolute
  locations - Not Relative.
• A map captured in the units of the paper sheet on
  which it is printed is based on relative
  locations on the map.
• In a coordinate system, the x-direction value is
  the easting and the y-direction value is the
  northing. Most systems make both values positive.

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Coordinate Systems and Projections Work Together

• To compare or edge-match maps in a GIS, both maps
  MUST be in the same coordinate system.
• To compare or edge-match maps in a GIS, both maps
  MUST be in the same projection.

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Data Exchange Bottom line

• Understand what the systems are and know what
  your GIS package accepts.
• To transfer data it is necessary to know
• What coordinates your data is in
• What projection your data is in
• What the datum is
• What units the data are in.

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Two Storage Models for GIS

• Vector
• Raster

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Topology - What in the heck is that dang deal?

• Topology is the property that describes the
  adjacency, and connectivity of features.

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TopologyWhy We Need It

• Topology allows automated error detection and
  elimination.
• Digitized or imported data must have
  topologically built.
• A GIS has to be able to build topology from
  unconnected arcs.
• Nodes that are close together can be "snapped" to
  establish a connection.
• Slivers due to double digitizing and overlay are
  eliminated.

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Prepare the Data Topologically

• Graphic Editing
• Snapping
• Dangle
• Slivers
• Undershoots
• Overshoots
• Intersections
• Open polygons

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Data Verification

• Cleanup of lines and junctions.
• Weeding of excess coordinates.
• Correction for distortion and warping.
• rubber sheeting.
• Construction of polygons.
• The addition of unique identifiers or labels.

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Where to Obtain Spatial Data

• Data Vendors
• USGS other Govt. Entities
• WWW
• Data Conversion Effort
• Gather data in the field manually,remote sensing,
  digital

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Methods to Capture GIS Data

• Manual digitizing
• Scanning
• C O G O
• Conversion of existing digital data.
• GPS Collection RTKS Post processing
• Remote Sensing

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Data Issues

• Incomplete spatial data.
• Locational placement errors of spatial data.
• Distortion of the spatial data.
• Incorrect linkages between spatial and attribute
  data.
• Attribute data is wrong or incomplete.

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WHY Statistics...

• Make Predictions
• Realize Probabilities
• Understand Distributions
• Model our World More Realistically
• What are the Extremes?
• Highs and Lows
• Determine good from bad data
• Reliability

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QUESTIONS ?