Using Presentational techniques in Geography

What are techniques of presentation? Generally these come from the list of cartographic( map) and graphical skills on the specification

Cartographic techniques include… ATLAS MAPS ORDNANCE SURVEY MAPS SKETCH MAPS FLOW LINES DESIRE LINES TRIP LINES CHOROPLETH MAPS ISOLINE MAPS DOT MAPS…

Graphical techniques include.. LINE GRAPHS BAR CHARTS SCATTERGRAPHS PIE CHARTS AND PROPORTIONALCIRCLES TRIANGULAR GRAPHS RADIAL DIAGRAMS LOGARITHMIC GRAPHS DISPERSION DIAGRAMS KITE DIAGRAMS..

CARTOGRAPHICAL MAPS Dot maps: Advantages and disadvantages?

What are dot maps and why are they used? Dot maps are useful ways of showing the density of a particular variable such as population. They can also indicate the distribution of a particular variable. Unlike a choropleth map, it is possible to estimate the numbers in a particular place, provided that each dot is clearly visible.

Dot maps- strengths and weaknesses Good Spatial -show density and distribution Accurate- can use a scale e.g. one dot represents 10 students Easy to plot Bad Clustering may make it impossible to plot and interpret e.g. in urban areas as the dots may begin to ‘merge’ Exact numbers on the map= impossible to calculate Can be misleading when there is a large difference in densities between places. Scale can be a problem e.g if each dot = 100,000 people, areas that are more sparse than this would not receive a dot, implying that nobody lived there at all…not necessarily true.

What’s the difference? Linear scale( arithmetic) graphs are useful when you want to show absolute changes in the data. The scale chosen should always allow the FULL RANGE OF DATA TO BE PLOTTED FOR EACH VARIABLE. A logarithmic graph is drawn as an arithmetic line graph Except that the SCALES ARE DIVIDED INTO A NUMBER OF CYCLES, EACH REPRESENTING A X 10 INCREASE IN THE RANGE OF VALUES. Logarithmic graphs are good for showing rates of change ( the steeper the line, the faster the rate) and they also ALLOW A WIDER RANGE OF DATA TO BE DISPLAYED.

What are logarithmic scales are why are they used? Logarithmic scales are a specialised variation of a line graph. The difference is that the scale is not even( as it is with an arithmetic/ linear scale) Where an arithmetic scale generally shows increases at equal intervals, a logarithmic scale does not. Instead, it uses a series of cycles( usually 3 or 4) where increases occur in multiples of 10.

What is a logarithmic scale. Why do geographers use this What is a logarithmic scale? Why do geographers use this? Advantages and Disadvantages?

So what’s the difference between semi- log and log-log graphs?

What is the difference between log- log and semi- log scales? Log- log graphs use the logarithmic scale on both the x and y axis. Semi- log graphs only use the logarithmic scale on the y axis. Instead, the x axis is an arithmetic scale.(This is particularly useful if you are interested in displaying data with a large range of values and if you are interested in change over time)

Strengths and weaknesses of logarithmic scales Good: For data with a very large range of values Useful for showing rate of change- a steeper line suggests a faster rate of change Bad: Easy to make errors plotting Zero cannot be plotted Negative and positive values cannot be displayed on the same graph.

Let’s revise the Hjulstrom curve

Bar charts/graphs Look at the bar chart below..Hum…!!

Is this bar graph good or bad?

Bar graphs: pros and cons Good show relationships between 2 or more variables show proportions visually attractive bars used combinations of qualitative and quantitative variables Can show positive and negative values Simple to construct and read Bad Plotting too many bars makes it appear cluttered- less easy to interpret If wide range of data impact lost as it is difficult to read accurately Become more complicated if uneven class intervals Using too many or too few classes can mask important patterns in the data

What does this graph show? What type of graph is this? A scattergraph

What is a scattergraph used for? (see pink booklet p.28) A scattergraph is a type of graph in which plotted points often appear as dots scattered across the graph paper. It is the simplest and most visual way in which to show correlation. You would use this technique when investigating relationships between two variables.

Scattergraphs:pros 1.Useful when considering two variables such as discharge of a river and distance downstream 2.Used when data is available for many locations (e.g individual river sites could be compared) 3.Shows anomalies 4.Trends indicated by best fit line 5.Correlations easily seen by direction of best fit line E.g. Blencathra river study ( see cream booklet for how to construct and usefulness of technique)

Scattergraphs - cons Does not show statistical strength of relationships Only two variables presented at any one time- can be seen to be limiting

Pie charts

Pros and cons of pie charts: Bad: Less than 3 segments look simplistic If many segments a similar size; it is hard to interpret Good: visually attractive shows proportion of components clearly using % totals shows scale

Proportional circles

Using Proportional Symbols Proportional circles are just one way that geographical features may be represented on a map. Other symbols may also be used , e.g squares, triangles and so on ( see map) . In each case it is essential that the SIZE of the SYMBOL is PROPORTIONAL to the VALUE IT REPRESENTS

Proportional circles Good visually attractive location shown provide context show scale show proportions Allows comparisons between data sets Bad Very hard to calculate Size may obscure location or mean less accurate positioning on maps, i.e. in cities

Consider this example: to display the composition clay , silt and sand in a soil sample:

Triangular Graphs Why useful? Triangular graphs are useful in showing the clustering between three different variables ( e.g. the different percentages of clay, silt and sand in a soil sample) They only work where the variables are given in percentage( %) form

Radial diagram- what does this show?

What is a radial diagram? Radial diagrams are used to plot data in a circular fashion around a central point, usually ( but not always!) reflecting compass bearings. Radial diagrams come in many different forms and examples include i) a wind rose diagram( which can be used to plot wind direction) ii) a polar graph, which can be used to display changing activity over different time periods( e.g. pedestrian flows over a 24 hr period)

Radial Diagram showing strength and direction of wind speed

Radial diagrams Good: Visual impact- easy to see patterns Spatial- directional Useful to show changes over time Bad: Hard to plot

Radial Diagram From what direction is the prevailing ( most common) wind in Washington state shown on the diagram? South Roughly what percentage of wind is westerly? 3.5%

DISPERSION DIAGRAM

What are Dispersion Diagrams and why are they useful? Dispersion diagrams allow you to investigate the spread of a set of data By plotting all of the data set on a vertical axis, the range within the data set becomes visually apparent. It is also possible to identify any clustering within the data set The data set has usually been plotted around the median value It is also possible to calculate the mean, mode,lower, upper and interquartile ranges and standard deviation for the data set

The ‘dispersion of data’ means the spread of data around the mean(average) What are mean, mode and median? What is the range? What does interquartile range mean?…….

Advantages of Dispersion Diagrams 1. Shows clearly the spread of data from the mean 2. Clear visual representation of the data 3. Gives a clear indication of the reliability of the data 4. Makes it possible to calculate the mean, median, mode, lower quartile, upper quartile, interquartile range and standard deviation 5. Can compare graphs easily 6. Anomalies can easily be identified

Disadvantages of Dispersion Diagrams 1. Only really works with a large data set 2. They are only really useful to display ONE DATA SET at a time 3. If you want to compare many different data sets it is quite a time consuming technique

Cartographic techniques include… ATLAS MAPS ORDNANCE SURVEY MAPS SKETCH MAPS FLOW LINES DESIRE LINES TRIP LINES CHOROPLETH MAPS ISOLINE MAPS DOT MAPS…

Flow line map

Why is the thickness of the arrows important Why is the thickness of the arrows important? What is the route of travel?

Why are flow lines used on maps? 1.A flow line is used on a map to show the actual flow and direction of something ( e.g. traffic) 2.The flow line is drawn proportional to the number travelling along the actual route by the use of a suitable scale. 3.Flow lines are more likely to be used on large scale maps ( see previous maps)

Strengths and weaknesses of Flow line maps: Good Straight forward visual impression Can see sequences- e.g. how tributaries feed main rivers Scale / width of lines shows proportions TASK: TRY Q 6ai) Bad In order to achieve a clear image Real distance is distorted Direction is distorted

Desire lines on maps

Why are desire lines used on maps? 1. Desire lines are lines on maps which are drawn directly from the point of origin and which take no account of a specific route or direction. 2. They are similar to flow lines, however, in that the width of the line is proportional to the quantity of movement . 3. You may have used them for CA at GCSE?!........ 4. Desire lines are usually drawn on smaller scale maps showing movement between regions or even different parts of the world.

Strengths and weaknesses of desire line maps Good Easy to construct Easy to interpret Good to show spatial awareness on map- straight lines represent the movement of goods or people from a regions to a central point Bad Maps can become easily crowded and complex if large amounts of data are to be plotted( N.B The problem can be overcome by drawing a closed circle around the destination point and then excluding all desire lines that fall within this circle) Does not show actual route TASK: TRY Q 2

Trip lines to show journey directions home after work:

Trip lines Trip lines are a variation on the desire lines concept. They are used to display information related to the trips or journeys taken by individual people, say home from work. On a map, trip lines look like spokes on a wheel.

Strengths and weaknesses of trip lines Good Easy to visualise and interpret All trip lines come from one central point so variation from this point can easily be identified E.g. it is possible to see the sphere of influence of Much Wenlock ( see previous map) Bad No way of displaying density as lines are all the same width Does not take individual routes into account

Isoline maps

What are isolines on maps? Isolines are lines that represent the same value along their whole length.( ‘iso’ means ‘the same’) You will have come across them before in geography e.g. Contour lines Weather maps( isobars) In CA work when presenting pedestrian flows River depth data( isovels)

Isovels to show changing velocity measurements along a straight river cross section

Isovels to show changing velocity measurements along an asymmetric meander cross section

Isolines on maps: Strengths and weaknesses Good Spatial Represent equal values along their length. Can keep point information as well for accuracy on map Can add colour- density shading to enhance patterns/ trends Bad Allow flexible interpretation of data There may be errors in the plotting TASK: June 2011 Q 1bi) and bii) N.B SEE EXAMINERS REPORT FOR ERRORS!!!!!!!!!!!!

2. Choropleth Maps

What is a choropleth map? Choropleth mapping is one of the most widely used techniques in displaying geographical data( e.g population densities, rates of disease etc..) The technique works by using a system of colour, grey scale or line density to show how the density of your data changes from place to place…

Choropleth Maps Good visually effective – reader can see general patterns location shown provide context show scale show densities Easy to construct Bad Map assumes the whole area has the same value, but there could be important variations Abrupt changes in boundaries- realistically would merge, therefore are not accurate