Geography - Maps and Cartography Flashcards
What defines a geographical entity?
Location (spatial reference)
This may be as an absolute or relative location
Dimensions
Size, shape
Attribute
Name, magnitude (e.g. temperature, value, population)
Time
When – important so that change / trends can be analysed
How can spatial data be collected or represented?
Points
Lines
Polygons / areas
Continuous surfaces
What’s so special about spatial data?
Geographic (spatial) data is multi dimensional
There are lots of it – it is voluminous
It can be represented / viewed at multiple scales
It requires a projection system to turn a 3D real world into a 2D computer model or paper map
Special analysis techniques are required – nearest, furthest etc
It can be laborious and time consuming to collect, process and analyses
It is expensive and complex to maintain up to date geographic data
What is a map?
Maps are a model of the ‘real World’ (or real World phenomena)
They have many purposes, but primarily communication
They require abstraction / generalization
What roles do maps have in society?
Means of communication
Means of navigation
Storage medium for spatial (and other) information
Provides a picture that allows analysis of spatial relationships, patterns and complexity
Maps as power
Ownership and economic value
Geopolitical power
How do maps help with communication?
Maps should capture the spatial character of the area to help the reader understand the geographical relationships between objects/areas
Cartography should be able to communicate this information
A map designer (cartographer) should consider how best to represent spatial data so that users can retrieve the desired information
What is the earliest evidence of maps?
Earliest evidence of maps comes from clay tablets, dated to pre 4000 BP
Give an example of mapping for science.
2500BP - Erastothenes calculated the circumference of the Earth using angular measurements
Give a brief overview of Ptolemy.
Claudius Ptolemaeus wrote a ‘Guide to Geography’ (~150 AD)
A systematic set of tables, distances and geographical information (not maps – but turned into maps later) – a ‘digital’ revolution before its time!
Proposed a system of projections and coordinate systems (still the basis of today’s systems)
QUOTE
“these things belong to the loftiest and loveliest of intellectual pursuits, namely to exhibit to human understanding through mathematics……the nature of the earth through a portrait since the real earth, being enormous and not surrounding us, cannot be inspected by any one person either as a whole or part by part” Ptolemy (Geography – 150AD)
What maps have been shown as a sign of power?
A T-O Map, that was first printed in the 13th century
What is a T-O map?
This is a map defined by theology, rather than geography, where place is understood through faith rather than location, and time according to biblical events (Brotton, 2012)
Hereford Mappamundi
c.1300
What maps have illustrated property and land ownership?
With the rise of agriculture, humans settled more permanently and used maps to delineate property and ownership.
This mappiform example is from Valcamonica in Italy, dated as around 3000 years BP, shows fields and houses carved on rock.
The carvings have been traced out onto an overlay. The interpretation is one of property ownership and control of the land.
What are modern cadastral maps?
Managed in the UK by Land Registry (England & Wales)
A source of record as to who owns what and when
What are way-finding and navigational maps?
These stick-maps (mattang) were used, and were still in use until recently, in Polynesia.
They are a way-finding tool to navigate between islands using swell waves refracted by the islands.
They were traditionally never taken to sea, but memorised.
What is another example of way-finding and navigational maps?
Another navigational device from Ammassalik, Greenland/ Kalaallit Nunaat (1880) given to Gustav Holm (with instructions).
Carved pieces of wood (wood floats) to help navigate the fjords when sea-fishing.
Who was Gerardus Mercator, and what was his significance to mapping?
Mercator devised a system of projecting the spheroid of the World onto a flat piece of paper – a way of visualising the World that we still use and recognise today – e.g. Google Maps/earth etc
Summarise Spatial Data.
Spatial data require ‘special’ considerations
The use of spatial data informs geographical knowledge and mapping communicates this data
Maps are designed to communicate spatial information for many purposes – cartography is, therefore, not just a simple process, but an art, a science and an evolving technology.
What are maps?
Maps are ‘abstractions’ to produce a model of reality (usually to some form of scale)
What do maps require?
Selection Classification Simplification Exaggeration Symbolization
What is map design?
Map design is primarily a function of the purpose (as well as who is making the map).
What functions can maps be grouped by?
General purpose or reference maps
e.g. atlas maps, topographic maps (e.g. Ordnance Survey)
Special purpose maps
e.g. Navigation maps, cadastral maps
Thematic maps
e.g. land cover, numerical data, qualitative data
What purposes are thematic maps produced for?
To provide information on what, and often how much of something is present (i.e. data storage / repository)
To map the characteristics of a phenomena, revealing a spatial order and/or organisation (visualisation)
To present findings to an audience (communication)
Give an example of geovisualisation.
MacEachren’s ‘cartography-cubed’ model – visualization is private, interactive and reveals unknowns; communication is public, non-interactive and reveals knowns
What are the general principles of map designs?
Map layout Scale and generalisation Symbolisation Classification – chloropleth mapping Colour Labelling
What is the link with gestalt in mapping?
Maps consists of elements
Human cognition is based on clumping
Elements seen both individually and holistically
Eye seeks similarity, proximity, continuity, closure
Symmetry, simplicity, balance favoured
By convention, what should maps include?
Title
Legend
Indication of scale
Orientation
Arrangements of objects around a ‘natural centre’
What was considered a response to Eurocentrism?
McArthur’s Universal Corrective Map of the World 1979
Where should the prime meridian be?
The zero line of longitude could have been placed anywhere on the globe.
International Meridian Conference voted on Greenwich in 1884.
Many World maps centre on Greenwich, which shows Europe as taking centre place, usually in conjunction with a Europe-enlarging Mercator projection!
What countries tend to use the International Dateline?
Centring of world maps on the international dateline is common practice in Australia, Japan, Malaysia, Indonesia and China, naturally.
What is the Cartographic Scale?
Cartographic scale is the relationship (ratio) of map or distance to the Earth’s surface depicted in a representation
What is meant by generalisation?
Maps are not photographs
When choosing a scale for a map, one has to decide on the level of generalisation
What you leave out should not be for ‘political reasons’
What is meant by choropleth Maps?
A map in which shaded areal symbols represent the magnitude of an attribute
Area is divided into regions /polygons for which data are collected – typically administrative, political or ‘natural’ boundaries
Perhaps the most widely used form of thematic map
Relatively easy to create
Relatively easy to interpret
Works well, as long as its weaknesses are recognized and efforts are made to minimize them
Give an example of a choropleth map.
A time-series of choropleth maps used to display public attitude to government spending on health care for the uninsured in the US in 2004, grouped by age and income of the respondents.
What is a disadvantage of a choropleth map?
Gives the impression that a feature or phenomenon is uniformly distributed within each enumeration unit
What is slocum’s design process?
Choose reproduction method
Select scale and projection appropriate for theme
Classification and symbolization method
Select map elements required
Rank symbols and elements into an “intellectual hierarchy”
Create a sketch map for design experiments
Test map on audience before making final version
Summarise: what’s in a map.
Good design makes map more effective and interpretable
Eye seeks similarity, proximity, continuity, closure
Symmetry, simplicity, balance favoured
Figure—ground
Alignment, balanced layout
Follow convention, except when you want to emphasize or challenge
When in doubt, reduce complexity
What is geo-location?
All spatial data have a location, whether absolute (tied to a coordinate system) or relative.
Absolute location can be determined through:
Angular measure of latitude and longitude
From a map (stated in the coordinate system of that map)
Using satellite positioning technology (e.g. GPS)
What is meant by longitude and latitude?
The Earth is not a perfect sphere – but an ellipsoid or geoid.
Latitude and longitude are essentially an angular measure from the centre of the Earth to the spheroid model.
Reported as an angle (degrees, minutes & seconds).
Depicted as lines of latitude and longitude.
What are map projections?
Mathematically it is not possible to ‘flatten’ a spheroid from a 3D shape, to a 2D representation
Therefore – all maps contain errors
Best approximations are through mathematical transformations – map projections
What do map projections seek to minimise error in?
Distance
Area
Direction
Scale
What is the difference between a Mercator Projection and a Sinusoidal Equal-Area?
MP = Preserves scale only at the equator, but bearings are correct
SEA = An equal area projection where shape is preserved only along Greenwich Meridian
What is significant with Map Coordinate Systems?
Essentially a grid system based upon a map projection
All have a ‘datum’ – a zero / zero coordinate
Map coordinates (grid references) are then determined based upon how far east / north of the datum you are located.
What is significant about Satellite Positioning Systems?
A Constellation of Earth-orbiting satellites for the purpose of defining geographic positions on and above the surface of the Earth.
First GPS satellite launched in 1978 - Full constellation achieved in 1994
Now also GLONASS (Russian) and soon Galileo (EU)
What are other forms of geo-location?
Postcodes / identifiers
IP / WiFi
GSM location
Participatory mapping
Summarise geo-locations.
Many spatial data have a ‘geo-location’ attached to them at the time of collection (e.g. GPS points).
Others do not, but have an identifier which can be turned into a geo-location (e.g. postcode).
Possible to fit geo-location to spatial data through processes of ‘geo-referencing’.
Geo-location can be defined as a map coordinate / lat/long angular measure – relatively straightforward to change between these.
Geo-location enables spatial data to be compared, merged, analysed, visualised…….especially within GIS environments……
What are remotely sensed data?
Acquired by some sort of scanning device that is not in contact with the object / area / phenomena that is being measured
Sensors usually mounted on an aircraft, drone, or satellite
Imaging sensors can scan a wide area:
Spatial resolution: size of discrete area scanned (pixel size)
Satellite-based sensors can either scan one area continuously (geostationary orbit) or build up a picture of the Earth scan by scan (polar orbiting)
What are most earth observation sensors?
Most Earth Observation sensors are ‘multispectral’ – acquire images simultaneously in different parts of the electro-magnetic spectrum:
Sensors image the Earth at different wavelengths of the spectrum – usually in multiple wavebands
What are the principles of remote sensing?
All objects will absorb, reflect or transmit electromagnetic radiation, creating a ‘spectral signature’
Multispectral remote sensing can detect this signature and:
Map ‘what is where’
Estimate properties of an object / phenomena
(e.g. concentration of biochemicals, temperature etc)
Monitor changes in ‘spectral signature’ to determine changing status / properties
What can we do by remote sensing air quality?
By remote sensing at specific wavelengths (parts of the electromagnetic spectrum) we can estimate the concentration of potentially harmful constituents of the atmosphere:
Ozone
Nitrous Oxide
particulate matter (smoke, dust, PM10 etc.)
Sulphur Dioxide
Summarise remote sensing.
Remote sensing is an important source of spatial data with respect to air quality
Synoptic (wide area) view rather than point source
Can scan on a frequent basis (each day, sometimes hourly) – detecting change
makes use of different parts of the electromagnetic spectrum to detect concentrations of atmospheric constituents
Remotely sensed data are one source of information, but extracting information and communicating that information requires GIS……
Provide an example of early spatial data.
Charles Booth’s poverty maps of London an early (1885) attempt to capture, store and analyse socio-economic geospatial data
Determined that 30% of London’s inhabitants lived below the poverty line
Provide an example of analysis of early spatial data.
Dr John Snow’s analysis of cholera in London (1854)
Map was segmented (Theissen polygons) which showed most deaths were clustered around the Broad Street water well.
In part, led to science of epidemiology (looking at (spatial) patterns of disease / infection and effects on human health)
