Thematic Mapping Flashcards
What are topographic maps a result of?
Land and air surveying. Primarily portraying topography (i.e. the configuration of the landscape).
What are topographic maps used for?
Engineering plans.
As well as a hard copy of a topographic map, what other form are they available in?
Available as databases.
How can topographic maps be presented?
Using GIS or CAD.
What does CAD stand for?
Computer-aided design.
Other than topographic name another type of map?
Thematic mapping.
What is a thematic map?
It is based on geographic distributions of a particular them, or relationship among a few selected themes such as population, rainfall, soil type etc.
Why is thematic mapping widespread?
1) Data availability
2) Powerful tool for visualising, analysis, decision making.
3) Easy to create within a GIS
What do we use qualitative data for?
To produce distribution maps such as points, paths and zones.
How can we produce categorical maps?
Using choropleth maps
What is special about choropleth maps?
Coloured in areas on a map.
What can we use a point distribution map for?
To represent all the bus stops in Tyne and Wear.
What can we use a path distribution map for?
All the A roads in and around Newcastle and Tyne and Wear,
When we download a backdrop from digimap what is the main purpose?
To display.
How can we make the thematic map more important that the context?
By reducing the transparency or brightness of the underlying contextual map or tuning into a grey scale image and toning it down so our thematic map is more important than the context.
What will it depend on when representing a set of values spatially?
The message you are trying to get across, the data you are starting with and the scale you are trying to represent the data.
How do you represent a set of value spatially?
Through a point density map or a dot density map where we assign a unit value to each of the dots.
When are point density maps effective?
When you have data that is stretched out of a large area as you get a good representation of the overall population density from this type of mapping.
What does dot mapping use?
Symbols with an assigned unit value. It uses the repetition principle.
What is the arrangement of the dots in dot mapping?
Can be regular or irregular arranged.
What is the disadvantage for a dot map?
Can be hard to interpret.
What are graduated symbols?
Where the size of the symbols varies, but categories (classes) devised.
What are proportional symbols?
Continuous variation, data measured as zero means no symbol.
What are the advantages and disadvantages of a proportional symbol?
They are a more exact representation but hard to tell subtle differences.
What are the advantages of a graduated symbol?
They are easier to distinguish one class to another depending on data.
What is the problem with quantitative data?
You can only show one quantity.
What can you create with quantitative data?
Cart-devised symbols- such as pie graphs, bar charts, stacks and they can all be 3D.
What is necessary to represent on a map?
A copyright statement.
Give an example of quantitative zonal mapping.
Isoline maps (surfaces).
What can describe surfaces as in an Isoline map?
Continuous
What is an Isoline similar to?
Contours
What does an Isoline produce/use?
Chorisogram
What is a choropleth map?
Imagine “stepped surface” of prisms defined by values for each unit area, where there is an implication of evenness in each area.
What is the problem with choropleth maps?
Addressing the type of data and the areal boundaries.
What do contour lines tell you?
The height above sea level.
When do we use normalisation?
Used to manipulate data more sensibly (especially choropleth mapping).
What is the phase when you classify quantitative data?
Binning
What can you do within the classification setting?
Edit class boundaries, constant or variable, based on counts, values or statistical measures.
What is the default for classifying quantitative data in ArcGIS?
Natural Breaks
What is natural breaks made up of?
5 classes maximises the differences between classes.
When is it good to use natural breaks?
When you have normally distributed data.
What is equal interval?
Interval calculated by number classes.
What is there an emphasis on withe equal interval?
The amount of an attribute value relative to other values.
When is equal interval used?
It is applied with familiar data ranges such as percentages and temperature.
What is quantile classification?
Each class contain an equal number of features.
When do we use quantile classification?
Linear distributed data.
How are features grouped in quantile classification?
By the number of classes in each class.
Where can features with widely different value be put?
In the same class.
How can you minimise distortion?
By increasing the number of classes.
What does standard deviation show us?
How much a features attribute value varies from the mean.
What helps us emphasis values above and below the mean?
A two-colour ramp.
How are outlier in our data removed?
1) Through a definition query
2) Through creating permanent subset
3) Through exclusion
What can manual classification do?
Adjust the boundaries anywhere you want.
What is manual classification?
You can drag lines on a graph or type in numbers in break values.
What should a value only belong to when thinking about legend presentation?
one class: 1-9, 10-19, 20-29, etc
How can you add understanding when creating a legend?
Add supplementary map face text.
Complete the phase “the more class the…….”
more uniform map appearance regardless of classification.
What is the maximum number of class you would have on a map?
7
