Graphs and charts

• Key terminology

  • continuous data, numerical data that can take any value within a given range like heights and weights.
  • discrete data, numerical data that can only take certain values.
  • quantitative data, results that can be expressed using numerical values.
  • qualitative data, results that can't be expressed as numbers.
• Line graph

  • displays continuous data, both axes are numerical and continuous, shows changes over time and space.
  • shows trends and patterns clearly, quicker and easier to construct than bar graphs, easy to interpret, anomalies are easy to identify.
  • does not show causes or effects, can be misleading if the scales on the axis are altered, if there are multiple lines on a graph it can confusing, often requires additional information to be useful.

  
• Bar chart

  • simplest form of displaying data, useful for comparing classes or groups of data and changes over time, the data is discrete.
  • summarises a large set of data, easy to interpret and construct, shows trends clearly.
  • requires additional information, does not show causes effects or patters, can be too simplistic, can only be used with discrete data.

  
• Histograms

  • show continuous data.
  • large data sets can be graphed easily, you can compare data.
  • they can only be used for numerical data, can be difficult to pinpoint exact data values.

  
• Population pyramid

  • a type of histogram, used to show the age-sex of a population, can be used to show the structure of an area or country.
  • easy to compare age and sex data, easy to read and annotate.
  • can take a long time to construct, detail cab be lost in the data, additional annotations may be necessary.

  
• Choropleth map

  • annual precipitation, population density, income levels.
  • clear visual representation of the changes over space, shows a larger amount of data, groupings are flexible.
  • makes it seem as if there is an abrupt change in the boundary, distinguishing between shades can be difficult, variations within the value set are not visible.

  
• Proportional symbols map

  • symbols are drawn in proportion to the variable, population, wind farms and electricity they gain, traffic or pedestrian flows.
  • illustrates the differences between many places, easy to read, data is specific to particular locations.
  • not easy to calculate the actual value, time-consuming to construct, positioning on a map may be difficult, particularly with larger symbols.