Basically interaction matrix is a two-dimensional listing, row listing and vertical listing constitutes impact interaction between each elements of characteristics and conditions of the environment and proposed actions that may affect the environment.
Since I have not made a picture for this, let me try to express this with words. Let us say the matrix consists of x axis and y ordinate. Factors for y ordinate for a project building a shopping mall include
As x axis, we may put detailed proposed actions such as
The principle is similar with checklist method, the interactions are measured in terms of magnitude and importance. The magnitudes represent the degree of the interaction between the environmental condition and the proposed actions. The importance of the interaction, is often considered as a judgement call, this is greatly influenced by the characteristic of engineering field, so this is part of engineer judgement.
If an interaction is present, for example between surface water and field opening, a diagonal line is put in the block and values are assigned for that particular element, with scale number. Number 1 is usually considered to be small impact and 5 is the biggest of magnitude or importance. Usually the action to open a new field area will make a significant impact, thus the magnitude and importance is large, we may assign 3/5 in the block, means the magnitude is moderatly big with largest importance.
We do the same thing for every elements using a great deal of judgement and even a personal bias. The number will then be summed over a line to give a numerical grade for either the proposed action or environmental elements (factors).
By trying this method, you will be able to find out advantage and disadvantage using this way, compare to checklist method. However, it must be noted that dealing with identifying elements need a search for a comprehensive, quantitative and interdisciplinary method for evaluating and judging environmental impact. And to some extent, this has led to the check list with weighted rangkings technique. I will cover this later. The fundamental intention is still to ensure that all aspects of the environment are covered, by giving these items a numerical rating in common units, so that comparison and brief picture of impact may be obtained.