Indicators may take many different forms – and part of the art of indicator development is to ensure that the right types, and an appropriate range and number, of indicators are selected to describe the issue of interest. 

Three different aspects of indicators need to be given particular attention:

• Position in causal chain – i.e. where within the chain from sources to impacts the indicators are targetted;
• Structure – i.e. how the indicators are constructed and their  associated level of complexity;
• Perspective – i.e. the value system from which the indicators are defined.