Line graphs

Line graphs⁵ are used when measurements are continuous, e.g. traffic, employment or river discharge (see Figure 6). They show the relationship between two variables, one of which causes the other to change, e.g. temperature and altitude. Altitude causes the temperature to change so it is the independent variable (x-axis), with temperature on the y-axis (dependent variable). If you have very large ranges on one single graph, e.g. 2-10,000 then consider using log or semi-log paper.

Fig. 6. Line graph showing changes in wind speed over 12 hours in three locations. Multiple data sets are displayed on the same axis which has been reseated to accommodate all data.

Bar graphs

In this type of bar graphs⁶ the horizontal x-axis represents a number of separate categories and the vertical axis shows the values or frequency (see Figure 7). Often a gap is left between bars (note that the computer won't do this automatically).

Fig. 7. Simple bar chart to show rainfall at a school weather station. Note how the bars are separated.

Histograms

In the case of a histogram, the horizontal axis represents a linked series of class intervals – normally continuous. It is not usual to leave spaces between bars in this instance (see Figure 8).

Fig. 8. Histogram showing results from a glacial sediment survey. Note how the к-axis data are linked or continuous.

Bar and histogram variants

Many variations of the traditional bar and histogram exist:

• mirror – bars drawn back to back (see Figure 9);

• population pyramids to show population structure by age;

• reverse bars – bars drawn below the x-axis to indicate a decrease in a particular category;

• proportional bars – show the proportion of change within component categories (see Figure 10).

Fig. 9. Bar graph with mirrored bars showing range and median bi-polar scores for various settlements in south Shropshire.

Fig. 10. Bar graph with proportional bars showing endangered animal species in Europe and central Asia.

Scattergraphs

Scattergraphs⁷ are used to explore the relationship between two variables – the pattern of the scatter shows the strength of the relationship and any anomalies in the data (see Figure 11). It is important to have sufficient data points so that meaningful interpretations can be made (at least 10).

Fig. 11. Scattergraph showing changes in channel width with increasing distance downstream. Note how the sites are not at regular intervals and the results have to be plotted accordingly. Site 11 appears to be an anomaly.

Pie charts

A pie chart⁸ is a circle divided into sectors proportional to the size of component categories in a given sample. You should use this type of graph when there are at least three but no more than eight different categories to display. It is normal practice to start with the largest category first and work clockwise round the circle in descending order. It is also possible to produce pies that are proportional in size to the size of the sample when comparing different sites or areas. 'Mini pies' can be very effective positioned on a base map (see Figure 12).

Fig. 12. Proportional pie charts on a base map indicating number of invertebrates caught at different river locations. Invertebrate species are an indicator of pollution.

Pictograms

A range of symbols (and part symbols) can be used to represent data (see Figure 13). These are a good idea in questionnaire surveys as they add variety, but they are less accurate than traditional bars or histograms.

Fig. 13. Pictogram showing methods of transport used by pupils.

Kite diagrams

If you are doing a vegetation project or footpath erosion survey, kite diagrams can be used to show change in a particular species along a transect (see Figures 14 and 15). It is often a good idea to stack kites vertically (with the graph paper turned sideways) so that comparisons can be made.

Fig. 14. Traditional kite diagram showing changes in plant cover across a footpath.

Fig. 15. Skeletal kite diagram of an interrupted transect on a saltmarsh. There arc significant distances (10 т or more) between sampling sites, so gaps are left between plot points.

Circular and rose graphs

Circular and rose graphs⁹ are used when the data take the form of compass directions (see Figure 16). They can he used to show wind direction, pebble orientation or orientation of glacial features. It is possible to construct this type of graph on a computer (often called a 'radial' plot), but make sure the scales are appropriate.

Fig. 16. Rose diagram showing orientation of stones at a sediment site.

Notes:

1. choropleth maps – карты ранжирования территории

2. topological map – карты доступности

3. proportional flow maps – графики мощности потока

4. dot maps – карты точечного показа

5. line graphs – линейные графики в системе координат

6. bar graphs – гистораммы

7. scattergraphs – графики рассеяния показателей

8. pie chart – диаграмма долевого участия

9. circular and rose graphs – роза ветров (направлений), индексетриссы рассеяния

Unit II

THE HISTORY OF EXPLORATION