1. Cartographic Concepts
Aim: to provide support staff with a basic knowledge of Cartographic Concepts
Digimap Training Workshops
Last Amended: 3 September 2001

2. Objectives By the end of this session you will:
be familiar with types of maps, their characteristics, projections on which they are based, and processes involved with their production
recognise large and small scale maps and understand level of detail that can be shown at each scale
be able to use information on maps to visualise, navigate, measure and locate features on the earth’s surface
Digimap Training Workshops
Last Amended: 3 September 2001

3. Basic characteristics of maps
maps are concerned with two elements:
location
positions in two-dimensional space
attributes
qualities or magnitudes
maps have a purpose
more in notes on purpose
Digimap Training Workshops
Last Amended: 3 September 2001

4. Categories of maps Topographic (General Reference Maps) Examples:
© Crown Copyright
Examples:
Street mapping
Hydographic charts
Orienteering
© Crown Copyright
Digimap Training Workshops
Last Amended: 3 September 2001

5. Categories of maps Thematic Examples: Election results Weather maps
Demographic (e.g. Census 2001)
Digimap Training Workshops
Last Amended: 3 September 2001

6. Map production – data collection & presentation
measurement
spatial
field survey (GPS, tape measure)
aerial photography
satellite imagery
attribute
questionnaire
field data collection (measurement)
graphics
Cartographic design
Digimap Training Workshops
Last Amended: 3 September 2001

7. Map production Printing Revision
one-off printing (e.g. by you, using Digimap)
bulk printing (e.g. by the Ordnance Survey)
Revision
Uses several techniques:
Global Positioning System (GPS)
Aerial photography
Detailed ground survey
Buy in other companies’ survey information
Digimap Training Workshops
Last Amended: 3 September 2001

8. Elements of maps the basic elements of a map are: scale map projection
spatial referencing system
features
generalisation
annotation
Digimap Training Workshops
Last Amended: 3 September 2001

9. Map scales any map is a scale representation of the Earth’s surface
scale may be defined as:
the ratio between distance measured on the map and the true distance on the ground
Digimap Training Workshops
Last Amended: 3 September 2001

10. Map scales scale may be expressed in several ways:
as a Representative Fraction
e.g. 1:1,250; 1:250,000; 1:63,360
“One unit on the map represents 1,250 units on the ground”
in words
e.g. “one inch to one mile”
“One inch on the map represents one mile on the ground”
by scale lines
100m 50
Digimap Training Workshops
Last Amended: 3 September 2001

11. Map scales large scale or small scale? relative terms: vary by subject
no absolute definition of large and small scale
Digimap Training Workshops
Last Amended: 3 September 2001

12. Map projections
a map projection transforms spatial relationships from a curved surface onto a flat plane using mathematical algorithms.
projections can be divided into 3 groups:
Cylindrical Azimuthal Conic
Digimap Training Workshops
Last Amended: 3 September 2001

13. Map projections GB Projection Height Datum
O.S. use a cylindrical projection called Transverse Mercator
Origin is 49 degrees north and 2 degrees west
Height Datum
Height information expressed as a measurement above a smooth assumed reference known as a Datum
usually Mean Sea Level at some point on coast
GB use Newlyn, Cornwall (Ordnance Datum)
France use Marseilles
Switzerland use Lake Geneva
Digimap Training Workshops
Last Amended: 3 September 2001

14. Referencing systems
to locate any point, feature or area on the Earth’s surface or a map it is necessary to have concepts and definitions of direction and distance
three main categories of referencing system:
Geographic (applies globally)
e.g. lines of latitude and longitude
Rectangular (applies locally)
e.g. Ordnance Survey National Grid system
non co-ordinate (applies locally)
e.g. Post Codes, Zip Codes
Digimap Training Workshops
Last Amended: 3 September 2001

15. Referencing systems Ordnance Survey National Grid
based on the Transverse Mercator Projection
origin off-set from 49° North, 2° West by 100km North and 400km West to ensure that the U.K. is covered by positive co-ordinates
this origin is as far south as the Scilly Isles and as far west as St Kilda
Digimap Training Workshops
Last Amended: 3 September 2001

16. Referencing systems - National Grid
Relationship between Transverse
Mercator graticule and O.S. National Grid System.
Red dot indicates true origin 49°N and 2°W
Green dot indicates false origin of GB National Grid, offset from true origin by 100km north and 400km west
Digimap Training Workshops
Last Amended: 3 September 2001

17. Referencing systems - National Grid
The UK is covered a by a 500 x 500 km square grid. This is a remnant of a previous referencing system.
Digimap Training Workshops
Last Amended: 3 September 2001

18. Referencing systems - National Grid
The grid is divided into 100 x 100km
squares each identified by two letters.
Note that the letter I is not used.
Digimap Training Workshops
Last Amended: 3 September 2001

19. Referencing systems - National Grid
Each 100km grid square is divided into100 x 10km squares.
These are from 0-9 from the SW corner left to right and from bottom to top.
Using this system we can identify a 10km grid square
e.g. TL63
Digimap Training Workshops
Last Amended: 3 September 2001

20. Referencing systems - National Grid6 4 3 7
The 10km grid square is divided
into 1km squares
Each is numbered as before from 0-9
Used in conjunction with the 10km grid square reference we can identify a 1km grid square
e.g. TL6432
Digimap Training Workshops
Last Amended: 3 September 2001

21. Referencing systems - National Grid
The 1km grid square is further divided into 100 metre squares.
Enables a more accurate reference to be provided. e.g. TL648321
The position of a point within square TL can be identified by adding extra digits.
Digimap Training Workshops
Last Amended: 3 September 2001

22. National Grid - Land-Line Tiles
For the purpose of identifying a grid square on a 1:1,250 plan, the 1km square is divided into 4 sections, NW, NE, SW and SE.
On a 1:1,250 plan the yellow square TL would appear on sheet TL6432SE
Digimap Training Workshops
Last Amended: 3 September 2001

23. Ordnance Survey Grid Reference Tutorial
Digimap Training Workshops

24. Geometric primitives all map symbols can be referred to as points
lines
areas
Digimap Training Workshops
Last Amended: 3 September 2001

25. Symbolisation
process of creating graphic symbols on a map to represent features that exist in the real world
symbols fall into two categories
Qualitative and Quantitative symbols
within these two categories are three sub-categories
point, line and area symbols
Digimap Training Workshops
Last Amended: 3 September 2001

26. Symbolisation Symbols vary by: Size Shape Colour Density Texture
Orientation
Digimap Training Workshops
Last Amended: 3 September 2001

27. Generalisation
scale of a map determines the amount of detail that may be shown
as the scale of the map is reduced the information that it shows becomes more generalised
Digimap Training Workshops
Last Amended: 3 September 2001

28. Generalisation Classification of a point pattern.
After clustering the points a single point is
selected, which does not have to coincide
with an existing point, to ‘typify’ the
cluster.
Digimap Training Workshops
Last Amended: 3 September 2001

29. Generalisation Simplification of buildings. Buildings are grouped
and their outline simplified whilst retaining their
general geographical characteristics.
Digimap Training Workshops
Last Amended: 3 September 2001

30. This feature has been simplified from an area to a point feature.
Generalisation
This feature has been simplified from an area to a point feature.
Digimap Training Workshops
Last Amended: 3 September 2001

31. Generalisation
200MB
6MB
The features on map A have been simplified to produce
map B whilst retaining all its main features. File size of digital
data will also be reduced.
Digimap Training Workshops
Last Amended: 3 September 2001

32. Text
text that appears on the face of the map is called annotation or cartographic text
distinctive text: place-names
descriptive text: e.g. Post Office
size, position and style imply importance, extent and nature of object
positioning conventions
Digimap Training Workshops
Last Amended: 3 September 2001

33. Maps components and marginalia
map marginalia
information printed around the margins of a map
assists with interpretation
major components
North point, scale indication, legend,
coordinate system: grid or graticule
map name
compilation and revision information
copyright statement
Digimap Training Workshops
Last Amended: 3 September 2001

34. Map Reading
a map may be regarded as a database from which geographical information may be extracted
when reading a map there are 4 stages of approach:
recognition stage
measurement stage
relationship stage
explanatory stage
Digimap Training Workshops
Last Amended: 3 September 2001