Isoline map

• Isoline maps show lines that join points of equal value.
• Isolines can only be used when the data (variables) to be plotted change gradually in the space where sufficient data has been gathered.
• Isolines show gradients - that is, the amount of change over a certain distance.
• Isolines closer together represent a high gradient, whereas isolines far apart represent a low gradient.
• In nature, gradients usually indicate a flow from higher values towards lower values.
• Isoline maps can simplify complex data to show gradual changes and patterns over large spatial areas.
• Isoline maps only work where there is plenty of data spread over the study area and the changes are gradual.
• Isoline maps can sometimes be difficult to distinguish the values of a certain point as you have to follow one of the isolines until you reach the value written on the line, of which can be difficult to read.
• Smaller isolines do not always have values written on them, so you need to read the value of a more important isoline (shown as a bold line) and then deduce the value of the smaller isoline. 
• Shading implies equal values between the isolines, sometimes in this area the points of data are guessed, which can be incorrect.
• Isoline maps avoid the problem of boundary lines
• Isoline maps can be easily drawn using computer software packages