RM Graphing Relationships PDF

Graphs 1: line graphs Different types of graph are used to represent statistical data. The most common types are line graphs, bar graphs and pie charts. Most graphs have two axes: the X axis is horizontal (across the bottom) while the Y axis is vertical (up the left side). The two axes...

Graphs 1: line graphs Different types of graph are used to represent statistical data. The most common types are line graphs, bar graphs and pie charts. Most graphs have two axes: the X axis is horizontal (across the bottom) while the Y axis is vertical (up the left side). The two axes each represent a different set of data. Line graphs are drawn by plotting points by their X and Y coordinates, then joining them together or drawing a line through the middle. The line graph below shows how energy consumption is expected to rise, while consumption of fossil fuels falls and the demand for renewable energy increases. Graphs 1: line graphs  Types of line graph Comparison Sometimes different sets of data will be represented on the same line graph, so comparisons can be made. This is sometimes called a comparison line graph. Compound If information can be subdivided into two (or more) types of data - e.g. total population growth, female population growth and male population growth - then all three can be drawn on a compound line graph. Scatter Where the points on a graph do not map into a neat line, a line is drawn through the middle of the points to show the trend or correlation. This is called a scatter graph.  Graphs 2: pie charts Pie charts are used for showing how something breaks down into its constituent parts. Pie charts are usually drawn so the biggest piece of pie comes first (starting at 12 o'clock). The 'others' section usually goes last (coming up to 12 o'clock). If each piece of pie has its percentage written in, it's easier for the reader to work out the exact proportions.  Graphs 2: pie charts The pie charts below show differences in the split between primary, secondary and tertiary employment in USA, Brazil and Nepal. Pie charts showing employment types in a given country.  Graphs 2: pie charts In the example on the previous page the circles are the same size. It would also have been possible to make the size of the circle proportional to the size of each country's labour market. Pie charts like this are sometimes called proportional circles.  Graphs 3: bar charts Bar charts or bar graphs represent data as vertical blocks or columns. The X axis shows what type of data each column represents, and the Y axis shows a value for that type of data. For example, in a rainfall graph, each column on the X axis represents a month of the year, with the height of each column on the Y axis showing the amount of rainfall in that month. Types of bar chart Compound It is possible to split each column into sections to show the breakdown of data. For example, the employment data shown on the previous page could have been represented as three columns on a bar chart. The three columns would represent the three countries, with each column subdivided into sections showing primary, secondary and tertiary in different colours. This type of bar chart is sometimes called a compound bar chart. Comparative It is also possible to compare two sets of data on a bar chart - for example, measuring rainfall in two countries over the same period. This type of bar graph is called a comparative bar graph.  Graphs 3: bar charts The chart below compares the tourism data for the UK in October 2001 with October the previous year. The graph shows how tourism declined after the terrorist attack in America in September 2001. Bar chart showing decline in tourism to the UK  Histogram A Histogram is a graphical display of data using bars of different heights. It is similar to a Bar Chart, but a histogram groups numbers into ranges  Histogram Histograms The following table shows the ages of 25 children on a school bus: Age Frequency 5-10 6 11-15 15 16-17 4 > 17 0 If we are going to draw a histogram to represent the data, we first need to find the class boundaries. In this case they are 5, 11, 16 and 18. The class widths are therefore 6, 5 and 2. The area of a histogram represents the frequency. The areas of our bars should therefore be 6, 15 and 4. Histogram  Histogram Remember that in a bar chart the height of the bar represents the frequency. It is therefore correct to label the vertical axis 'frequency'. However, as in a histogram, it is the area which represents the frequency. It would therefore be incorrect to label the vertical axis 'frequency' and the label should be 'frequency density'. So we know that Area = frequency = Frequency density x class width hence: Frequency density = frequency ÷ class width