GIS :: Spatial Data

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GIS Spatial Data
Class Presentation, Spring 2008 University of
California, Los Angeles Student Natalia
Vinnik Email nvinnik_at_cs.ucla.edu
http//eureka3d.com
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Spatial Data Outline

• General overview Example
• Characteristics of Spatial Data
• Spatial Referencing
• Entity Types
• Main GIS models
• Vector Model vs Raster Model
• Mapping process of spatial data
• Conclusion

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General Overview

• All Geographical Information Systems are computer
  representations of some aspect of the real world.
• Most of the information we have about our world
  contains a location reference, placing that
  information at some point on the globe.
• Spatial Data is a data that has information about
  the location, shape, and relationships among
  geographic features and usually stored as
  coordinates.
• All GIS software has been designed to handle
  spatial data (also referred to as geographical
  data).

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Example Happy Valley GIS

• Establish GIS to help improve quality of ski
  experience
• Spatial data that can be useful to find out
• Where particular features found? (Facilities,
  lifts, etc)
• What geographical patterns exists? (Patterns of
  accidents)
• Where have changes occurred over a given time
  period? (Picture of snow cover in GIS)
• Where do certain conditions apply? (wind
  strength, snow cover, avalanche danger, etc)

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Characteristics of Spatial Data
Spatial data is characterized by

• information about position
• Example Latitude and longitude as a
  geographical reference, that can be used to
  deduce relationships with nearby features of
  interest. (Weather stations)
• connections with other features
• Example To describe which roads, lifts and ski
  trails would allow the meteorologists access to
  the weather stations
• details of non-spatial characteristics
• Example details of the amount of snowfall,
  temperature, wind speed and direction

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Spatial Referencing

• It is a challenge to adopt a flexible and lasting
  referencing system.
• Two main approaches for representing geographical
  space occupied by spatial data

• Layer-Based Approach
• Tradition way
• Similar to cartographic maps that usually
  available for individual areas.
• It was a first method for modeling space that was
  developed.

http//www.monroecounty.gov
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Spatial Referencing

• Object-Oriented Approach
• Considers that space is populated by discrete
  objects
• Each of the objects is discrete
• There is empty space between the objects

• Example
• Telephone company needs to map and manage
  telephone poles, connection boxes and cables

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Entity Types

• To capture the real world precisely we need an
  infinitely large database.

Data must be somehow reduced to a finite and
manageable quantity by a process of
generalization or abstraction

• Three basic entity types
• Points single grid reference, simple location
• Lines linear features
• Areas geographical zones
• (artificial and observable)

All three entity types are used to represent
surfaces in GIS
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GIS Models Raster Model
Three basic entity types are used in two main
models in GIS
Raster Model

• Represents features as a matrix of cells in
  continuous space.
• It divides the entire study area into a regular
  grid of cells in specific sequence.
• Each layer represents one attribute.
• Raster files can be manipulated quickly by the
  computer
• They are often less detailed and may be less
  visually appealing
• Particularly applicable when remote sensed
  images are used.

Land cover classification
http//erg.usgs.gov/isb/pubs/gis_poster
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GIS Models Vector Model
Vector Model
Land cover classification

• All entity types are recorded in terms of
  their geographic x and y co-ordinates.
• Vector model is concerned with boundaries of
  represented objects
• Can approximate the appearance of more
  traditional hand-drafted maps.
• More appropriate for mapping discrete
  geographic entities such as road networks, river
  networks and administrative boundaries,
  particular housing subdivision

http//erg.usgs.gov/isb/pubs/gis_poster
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GIS Models Vector vs Raster

• Main Focus

• What it addresses

• Representation

• Accuracy of representation

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GIS Models Vector vs Raster

• Boundaries

• What it is used for

GIS can convert data between different formats.
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Mapping process of spatial data

• Establish purpose
• Define scale
• Select the features
• Choose method for representation
• Generalize features for 2D representation
• Adopt map projections
• Apply spatial referencing system
• Annotate

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Conclusion

• GIS deals with spatial data
• 3 main characteristics position, connections
  with other features and non-spatial details
• 2 main spatial referencing approaches
  layer-based and objected-oriented
• 3 basic entity types points, lines and areas
• 2 main GIS models Raster Model and Vector Model
• Raster model is easier but more generalized
• Vector model is more precise
• 8 main steps of mapping process find purpose,
  define scale, select features, choose method of
  representation, generalize, map projection, apply
  spatial referencing system and annotate.

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Questions?
Thank you
Student Natalia Vinnik Email nvinnik_at_cs.ucla.edu