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GIS 101: Introduction to Geographic Information Systems

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Map scale is based on the representative fraction, the ratio of a distance on ... preserves the area of a feature across the map is equal area or equivalent. ... – PowerPoint PPT presentation

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Title: GIS 101: Introduction to Geographic Information Systems


1
GIS 101 Introduction to Geographic Information
Systems
  • Week 6
  • GIS Databases and Effective Usage
  • Mid-Term Review

2
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

3
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.

4
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.

5
GIS Databases and Effective Usage
  • ESRI data models
  • ArcView Shapefiles
  • Arc/Info Coverages
  • ArcGIS Geodatabase Layers
  • Use of Spatial Database Engine (SDE)

6
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

7
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

8
What is a GIS?
  • ESRI a GIS is made up of Data, Software,
    Hardware, and People.
  • Some now add a fifth element Methods.

9
Cartography
  • The art, science, and craft of mapmaking.
  • Cartography is the science that deals with the
    construction, use, and principles behind maps.

10
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

11
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)

12
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.

13
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.

14
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.

15
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.

16
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.

17
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.

18
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.

19
Two Storage Models for GIS
  • Vector
  • Raster

20
Topology - What in the heck is that dang deal?
  • Topology is the property that describes the
    adjacency, and connectivity of features.

21
Topology Why 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.

22
Prepare the Data Topologically
  • Graphic Editing
  • Snapping
  • Dangle
  • Slivers
  • Undershoots
  • Overshoots
  • Intersections
  • Open polygons

23
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.

24
Where to Obtain Spatial Data
  • Data Vendors
  • USGS other Govt. Entities
  • WWW
  • Data Conversion Effort
  • Gather data in the field manually,remote sensing,
    digital

25
Methods to Capture GIS Data
  • Manual digitizing
  • Scanning
  • C O G O
  • Conversion of existing digital data.
  • GPS Collection RTKS Post processing
  • Remote Sensing

26
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.

27
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

28
QUESTIONS ?
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