Data is presented in graphs as information is easier to retain visually than as numbers or tables.

Graph theory is a branch of mathematics concerned with networks of points connected by lines. The subject of graph theory had its beginnings in recreational math problems, but it has grown into a significant area of mathematical research, with applications in chemistry, operations research, social sciences, and computer science.

The history of graph theory may be specifically traced to 1735, when the Swiss mathematician Leonhard Euler solved the Königsberg bridge problem. He created the first graph to simulate a real time, place and situation to solve a problem which was then considered one of the toughest problems. Yet from such deceptively simple origins, graph theory has grown into a powerful and deep mathematical theory with applications in the physical, biological, and social sciences.

The Königsberg bridge problem was an old puzzle concerning the possibility of finding a path over every one of seven bridges that span a forked river flowing past an island—but without crossing any bridge twice. Euler argued that no such path exists. His proof involved only references to the physical arrangement of the bridges, but essentially he proved the first theorem in graph theory. This is according to Britanicca.com.

According to iase-web.org, early graphics that were the basis of policy change were John Snow’s 1854 ‘Broad Street Map’ which was used to locate the origin of an outbreak of cholera in London and the 1858 ‘Rose’ of Florence Nightingale, a diagram of the causes of death in the Crimean war that showed that most soldiers were dying from preventable diseases not war injuries.

Many recent graphs however, that extend those that can be created in Excel have dynamic (play over time) and interactive features. Dynamic population pyramids and other interactive graphs are now routinely used by many national statistics offices.

Possibly the best known dynamic and interactive graph is Hans Rosling’s Gapminder (www.gapminder.org) that uses bubble graphs to display five variables simultaneously: region (colour), relative population size of a country (size of bubble), two other variables chosen from a set of OECD indicators (on the vertical and horizontal axes) and time (as the dynamic variable).

Graphs and maps are now being integrated with using Geographic Information Systems (GIS) software. However, as more and more graphs are produced we need to be sure that they are based on good, rather than bad, data and that the graph accurately represents the data