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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Referencing systems - National Grid 6 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

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 TL648321 can be identified by adding extra digits. Digimap Training Workshops Last Amended: 3 September 2001

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 TL648321 would appear on sheet TL6432SE Digimap Training Workshops Last Amended: 3 September 2001

Ordnance Survey Grid Reference Tutorial Digimap Training Workshops

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

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

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

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

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

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

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

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

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

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

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