# Centric Systematic Area Sampling

Surveyors should use as many quadrats as is feasible with the time and resources available for the survey. Any quadrats placed on the map which contain less than 50% of the survey area should be excluded. Calculating number of villages per quadrat: Once the number of quadrats is finalised, the surveyors should work out how many villages to select in each quadrat by dividing the recommended number of villages (n villages) by the number of quadrats. Therefore using the example from the previous page where a total of 35 villages needed to be sampled, the number of villages per quadrat for Figure 1 would be: $left lceil 35 div 8 right rceil = left lceil 4.38 right rceil = 5$ While the number of village per quadrat for Figure 2 would be: $left lceil 35 div 19 right rceil = left lceil 1.84 right rceil = 2$ The result of this formula should always be rounded up. Selection of villages in quadrats: With this number, the surveyors should select villages to sample in each quadrat and by drawing two lines across the centre of the box and selecting the correct number of villages closest to the centre. Figure 3 provides an example of this: