Geographic data

1
Geographic data
Geographic data are categorized on the basis of a
scaling system called levels of
measurement. There are four levels of
measurement.
2
Geographic levels of measurement

• Nominal data identification only, non-numerical

• Ordinal data ranked, non-numerical

• Interval data ranked on a standard scale where
  intervals between ranks are given in arbitrary
  standard units, e.g. Celsius temperature scale

• Ratio data numerical with a known starting point

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Data Unit of measurement Level of
measurement (Scale) Resort name identity nomi
nal Resort ranking position ordinal Average
winter ºC interval temperature Size of ski
area square metres ratio
Table 2.1 in Heywood et al
4

• Nominal data are qualitative in nature.
• Ordinal data are ranked.
• Interval and Ratio data are quantitative.

Map type or cartographic symbolization is linked
to whether the data are qualitative or
quantitative.
5
When data are qualitative, cartographic
symbolization uses shape, colour hue, and pattern
to differentiate features.
The original of this chart and the charts on the
following two slides are found at http//atlas.gc
.ca/site/english/learningresources/carto_corner/ma
p_content_carto_symbology.html3
6
When data are ranked, cartographic symbolization
uses size or weight, colour value or intensity,
and pattern to differentiate features.
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When data are quantitative, cartographic
symbolization uses size, thickness, and weight,
colour value, and colour intensity to
differentiate features.
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Shape
AV Map options
Data characteristics
1. no differentiation, base only 2.
identification only, nominal data 3. ordinal,
interval, or ratio
point or line
1. single symbol 2. unique value 3. graduated
symbol
variation in hue or symbol shape
variation in size
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Shape
Data characteristics
AV Map options
4. ordinal, interval, or ratio 5. interval, or
ratio
point or line
4. graduated colour 5. chart
variation in colour value or intensity
10
Shape
Data characteristics
AV Map options
1. no differentiation, base only 2.
identification only, nominal data 3. ordinal,
interval, or ratio
polygon
1. single symbol 2. unique value 3. graduated
colour
variation in hue
variation in colour value or intensity
11
Shape
Map options
Data characteristics
4. ratio 5. interval, or ratio
4. dot 5. chart
polygon
variation in unit quantity
12
Database management
Most GISs include a DBMS which allows searches of
the database and controls them. Then the users
do not need to know how the data are physically
stored and coded.
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DBMSs support retrieval functions in the form of
queries.
There are two general types of queries 1.
spatial queries what is here? 2. attribute
queries where is this?
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1. spatial queries what is here?
query the map (View)
2. attribute queries where is this?
query the database (Table)