This map shows the 815 generating stations with a capacity of 500 kilowatts or greater classed by the principal fuel used. Two fuels are dominant: water power (hydro-electricity) and petroleum products. The pattern of hydro plants across Canada is partly explained by Canada's geology: areas that are either rugged or mountainous should have more good sites for these plants than do flat-lying areas. The geology map of Canada has been added here confirms this: it shows that the Canadian Shield (rugged) and Orogen areas (mountainous areas) do have many more hydro stations than do platforms (flat-lying areas). For the other prominent fuel - petroleum products - it can be seen that a large number of plants in Canada's North operate on petroleum fuels.