Introduction to cartography geog 2016 e
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Introduction to Cartography GEOG 2016 E. Lecture-6 Data Processing and Classification. Cartographic Data Management. Management of data to produce a map consists of following steps: Selection Preliminary steps to gather the appropriate data. Classification Simplification

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Introduction to CartographyGEOG 2016 E

Lecture-6

Data Processing and Classification


Cartographic Data Management

  • Management of data to produce a map consists of following steps:

    • Selection

      • Preliminary steps to gather the appropriate data.

    • Classification

    • Simplification

      • These are the data processing steps.


Classification

  • Classification means grouping values into classes such that the required geographic patterns become prominent.


Class Boundaries – Equal Interval

  • Equal Interval

    • The whole range is divided into equal intervals called classes.

    • Each class is filled with the number of values found in the corresponding interval.

l1

l2

l3

l4

l5


Class Boundaries - Quantile

  • Quantile

    • Each class is creates such that it contains equal number of values.

    • The classes may have different widths.

a1

a2

a5

a4

a5


Class Boundaries – Natural Break

  • Natural Break

    • Class boundaries are choses when there is appreciable change in data.

    • Classes may have different widths.


Class Boundaries – Standard Deviation

  • Standard Deviation

    • Class boundaries are chosen with respect to deviation from the mean.

    • Classes may have different widths.

σ


Simplification

  • Simplification means changing geometry such that relevant details get pronounced and irrelevant details get suppressed.

Line Simplification

Area Simplification


Storing Information

  • To generate maps we need data.

  • These data can be in analog or digital form.

  • The generated map can also be in analog or digital form.

  • Analog

    • World is scaled to a miniature representation

    • A paper map is analog

  • Digital

    • Data and map are stored in computer memory

    • Manipulation and analysis of data and maps are possible


Geographic Information

  • A piece of geographic information can have location, time and attribute

  • Analog information

    • It’s cold today in Sudbury

  • Digital information

    • At 46.45783 degrees latitude and -81.00443 degrees longitude at 7 am the temperature was -10 degrees Celsius


Discrete Objects

  • Objects on a map are represented by points, lines and areas

  • These discrete objects can be stored in a digital database

  • They can then be:

    • Analyzed

    • Manipulated

    • Counted


Parameters

  • There are a number of parameters that are important in terms of geographic representation.

    • Temperature

    • Soil pH

    • Soil type

    • Land type

    • Elevation

    • Rainfall

    • Taxation rate

    • Population

    • ……


Geographic Representation

  • In geography each variable can be represented in different ways:

    • Polygons

    • Grids

    • TIN (Triangular Irregular Network)

    • Sample points

    • Contours


Spatial Data

Grid co-ordinate

Placename

Latitude / Longitude

Postcode

Description

Distance & bearing


Characteristics of Spatial Data

Geometry

  • The shape of a building or county

  • The course of a river, the route of a road

  • The shape of the landscape, relief


Characteristics of Spatial Data

  • Topology

    • Connected to

    • Within

    • Adjacent to

    • North of . . .

  • Example

    • Within the town of Lively

    • Opposite the Fraser building

    • South of main library

    • Adjacent to the Parker building


  • Data Modeling Steps

    • Identify the important features

    • Decide how you can best represent them: point, line, polygon

    • Find the important attributes related to all the features

    • Store information in a geographic database


    GIS VectorFormat

    GIS RasterFormat

    Map Feature

    (X,Y)Coordinate in space

    Cell Locatedin an Array

    Digital Data Formats

    • In geography, there are two main digital data formats:

      • Raster

      • Vector


    GIS VectorFormat

    GIS RasterFormat

    Map Feature

    Vector and Raster Representations


    GIS VectorFormat

    GIS RasterFormat

    Map Feature

    Vector and Raster Representations


    Comparison: Raster and Vector Formats

    Raster

    Vector

    • Raster formats are efficient when comparing information among arrays with the same cell size.

    • Raster files are generally very large because each cell occupies a separate line of data, only one attribute can be assigned to each cell, and cell sizes are relatively small.

    • Vector formats are efficient when comparing information whose geographical shapes and sizes are different.

    • Vector files are much smaller because a relatively small number of vectors can precisely describe large areas and many attributes can be ascribed to these areas.


    Digital Databases

    • There is no single database that can store every imaginable piece of geographic information.

    • Specialized databases have been developed to handle selected pieces of spatial data.

    • Some of these databases are in proprietary formats while others are in open formats.


    Thematic Database

    • A thematic database contains special datasets associated with a particular activity.

    • Soil Survey Geographic Database or SSURGO contains the attributes related to soil. This database has been developed by the Soil Conservation Service of the US Department of Agriculture.

    • Similarly, the National Wetland Inventory or NWI has constructed a database that contains information on wetland location and types.


    Digital Elevation Database

    • Digital Elevation Model or DEM consists of an array of regularly spaced elevations.

    • The United States Geological Survey or USGS provides a number of DEM databases with different array spacings and geographical coverages.

    • In Canada, GeoBase provides DEM in support from Natural Resources Canada.


    Digital Image Data

    • More and more governmental and private agencies are starting to provide digital imagery.

    • These photos are based on satellite and aerial photography


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