Presenting your data - Graphical skills

Technique When to use it Advantages Disadvantages Examples references

Complex techniques?

Pie chart Circles divided into sections ( component categories) used when there are 4 -5 of these

Quick to construct and easy to interpretGood impression of the relative proportion that go to make up the total. (% times 3.6 = degrees)

No good for more than 6 or more variables

SG P18Nagle P41Traffic counts, pedestrian counts,

Often used to compare two pie charts.Size of circle can be changed to make it a proportional pie chart which allows a comparison of the volume as well as the characteristics. ( could be linked to a base map)Pie charts over time is also valid use

Bar graph They have one quantitative scale ( often frequency)The horizontal scale does not have a numerical scale but has categories (places names etc)

One of the simplest ways of showing dataTypes :Simple – shoe one single factorCompound – sub division – v. effective showing two types of data

Needs at least 3 categories and no more than 5 or 6

SG P16Nagle P56-7

A divided bar chart can be used to show several sites on one graph for easy comparison. Each bar will be divided into sections to reflect the categories. By making each bar 100% you can then show how your categories change across sitesReverse bars - shows negative values as well as positive.

Histograms Similar to Bar graphs but have two quantitative scalesThe horizontal axis represents size of class

Often used as a starting point as measure of central tendency ( linked to mean mode modal class)

It is often difficult to decide on the modal class boundaries – which can crucially affect the shape of histogram

S&K p268-9 Histograms can have three types of shape – Normal ( bell shaped)/ Positive skew ( modal class is in lower classes) Positive skew ( modal class lies to the upper end of the distribution)

Line graph Another way of displaying numerical and categorical data.Most useful when data is continuous

Makes results sequential – showing peaks and troughs.Also gives visual impression of the actual rate of change

Can be difficult to construct if there is a wide range of data

SG p21Nagle P61 cumulative frequencyS&K P266 for log graphs

Problem of range can be overcome by using Logarithmic graph paperOther adv they can be used to compare rates of growth of variables.See also cumulative frequency graphs which can be used as first stage in

over time/space calculating Interquartile rangeScattergraph When you have two

sets of numerical data and want to look at relationships/correlation try to put the independent variable on horizontal axis – dependent variable that is being changed on vertical

Easy way to see if there is a relationship through a best fit line (trend line. Three types of pattern: Positive / negative /or no correlation. Anomalies (residuals) can be identified (ignored by best fit line)

Needs at least 10 data sets to be effective. Can be time consuming to construct

Nagle P51-53SG P17/35

Bedload size vs Distance downstream(see River Lemon work)

Spearman’s Rank Correlation Coefficient is a statistical test that often follows a scattergraph as is establishes if a relationship is statistically significant or not.Or the spearman is done first then the scattergraph follows.

Dispersion graph Used to show the spread of a number of values around the mean value.

They enable a comparison of the spread or bunching of data. Easy to compare mean mode median

Takes long time to plotScale issues ( might have to use semi log paper)

S&K P266SG P21/39River bedload size ( see River lemon work)

Often used as a prelude to statistical techniques such as calculation of upper and lower quartile and standard deviation

Triangular graphs Really a scattergraph that shows three sets of data

Large amount of data in one diagramAllows user to see how the variable are interrelated

Can be difficult to construct and read

SG P19/37S&K 264

Always look to the edges and see direction the numbers are running inTrial and error – remember the total of all three should add up to 100%

Kite diagrams Usually used to describe the distribution of different species along a transect

The kites represent the presence or absence of veg species

Limited applications S&K 264Sand dune succession

Can be put alongside other variables such as height, gradient soil type

Radial Diagrams Use polar coordinate graph paper related to the scattergraph and rose diagram

Useful when showing some data with orientation

Limited applications S&K P265Wind directionCorrie orientation

Continuous cycles – such as monthly progression in temperature regimes

Bi Polar diagrams Often used in questionnaires to

Coverts subjective opinion to objective

Dependent on personal judgement

Nagle P62-3 Often reluctance to use extremes of scale

measure env. quality data that it can be graphed

Presenting your data - Cartographic skills

Cartographic means presenting data or information in a map form. Maps are to show how things occur spatially. Much of Geography is about the description and explanation of SPATIAL DISTRIBUTIONS over the earth surface.

Technique When to use it Advantages Disadvantages Examples references

Complex techniques?

Dot Maps To show arrange of point located data e.g. farms/factories/weather stations

Good visual impression of distribution

1.Time consuming to plot2.All data points are assumed to be equal

Nagle P38 1.Disadvantage No2 might be resolved by using dots of more than one size2. A range of symbol ( not just dots could be used to show more than one distribution

Proportional symbols

If you have point data but wish to show not just distribution but also spatial variations in values

Allows a clear and quick way to show complex data. Can be easily added to a map as well

1 choosing a suitable scale for symbol – not too small but not too big so that it mergesCan be fiddly to draw and be consistent with scale

Nagle P39-40SG P11/31

1.To gain symbol area it may be necessary to square root the values2. Can be developed into a proportional pie chart with little extra effort.

Choropleth map Allows you to demonstrate different densities on a map ( i.e. average values per unit area )

Can give a striking visual impact. Able to see the general pattern of distribution( Should use one colour spectrumDo key first to check it works)

Can be misleading – false impression of abrupt change at the boundaries of each area, and of uniformity within the boundary ( when it is only an average – a generalisation)

SG P13 /31NagleP42

Population densities within or between countries,

Deciding on the class intervals can be crucial – can be done in several waysFirst rank data to get range- divide into 4-6 groups (by arithmetic breaks/geometric breaks/ natural breaks/equal number of values in each) The fewer the group the greater the generalisation the larger the number of groups the greater the complexity

Isoline map Lines joining places of equal valueIdentifies patterns in multiple data sets

Allows you to identify key areas. Shows trends over space and gradients between high and low values

Only valid if there is lots of points of data (small sets can be misleading)Assumes that between two observed values there are intermediate values that are never larger or smaller( interpolation)

Nagle p44SG P14/32-33River velocitypedestrian counts, Sphere of Influence

Shading can turn it into an Isopleth mapElement of personal judgement.

Flow lines Usually used to show where people have come from, along the actual route taken. The volume of movement between places. Thickness of the line indicates volume

Useful for showing flows – e.g. .traffic / discharge etc

Can become difficult to work out an appropriate width for the linesand keeping arrows clear when lots come from the same direction

SG p12/31Nagle P45

By varying the width of the arrow, you can show the volume of people coming from each direction. This becomes a proportional flow line map.

Desire line Similar to above butnot along actual route takenThe number of journeys is shown by lines of proportional thickness

Quick way to show on a map where a catchment area or sphere of influence

Can become very crowded and complex if large amounts of data are involved

S&K P257-8 Trip lines are the simplest of this group they are straight line is drawn to show each individual movement (journey) from a starting point to a central point

Annotated Sketch Maps/photo

A sketch is a rough drawing showing important information about an area

Provides a general impression

Limited application SG P7/28Nagle P45-6

Annotation very important – it labelling with attitude – i.e. detail often with possible explanation butavoid inessential extras

S&K = Smith and Knill (A2 text book) SG = 4A Study Guide( Philip Allen)