Introduction to CartographyGEOG 2016 E

Lecture-6Data 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

PlacenameGrid co-ordinate

Postcode

Distance & bearingDescription

Latitude / Longitude

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

Digital Data Formats

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

Map FeatureGIS Vector

Format GIS RasterFormat

(X,Y)Coordinate in space

Cell Locatedin an Array

Vector and Raster Representations

Map FeatureGIS Vector

FormatGIS Raster

Format

Vector and Raster Representations

Map FeatureGIS Vector

FormatGIS Raster

Format

Comparison: Raster and Vector Formats

• 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.

Raster Vector

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