# Determine carers willingness to walk to access services

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### Franck

Epidemiologist

Normal user

14 Feb 2013, 09:26

In Myatt, Mark et al. 2012. Semi-Quantitative Evaluation of Access and Coverage (SQUEAC)/Simplified Lot Quality Assurance Sampling Evaluation of Access and Coverage (SLEAC) Technical Reference (page 40) there are table after a mapping. Can anybody give me explanation on method used by the author to determine the numbers in colum ( Pair) and (d)

Thank you for your help

### Ernest Guevarra

Valid International

Technical expert

14 Feb 2013, 10:55

The column "Pair" refers to a pair of points on the map which refer to an area i.e. village, market, etc. The number in the column "Pair" is a label more than a numeric vector. So, it would read as "Pair 1", "Pair 2", "Pair 3" and so on. The column "d" is the distance between the two points in a pair. This would read as "The distance between the two points in Pair 1 is 21 kms". This is a numeric vector of distance in kilometres. The distance "d" can be calculated using the scale of the map being used and by measuring the distance between the points in a pair using a ruler. Appropriate calculations can be made to convert this measure using a ruler into the corresponding distance in kilometres.

For example, if the scale of the map is 1:50,000, this means that for every 1cm in the map, it corresponds to 50,000 cms in actual distance. 50,000 cms is equal to 0.5 kms.

So, if two points are 20 cms apart when measured on the map, the actual distance in kilometres can be calculated as:

1 cm 20 cm -------- = -------- ; x = 20 (0.5 km) = 10 kms 0.5 km x

So, the distance d between the two points is 10 kms.

There are other ways of calculating this distance depending on the geographic data that you have. For example, if you have GPS locations of points on the map, there are a lot of online applications that calculate these distances for you or you can apply simple coordinate geometry to get the difference between the two coordinates and come up with the distance.

I hope this answers your question.

### Mark Myatt

Consultant Epidemiologist, Brixton Health

Frequent user

14 Feb 2013, 13:22

The column "Pair" is a just a label, the column "d" is the distance between **adjacent** villages and towns with markets (these are the distances shown on the map). We take the mean "d" and divide by two to give an estimate at the largest distance that carers might be willing to walk to access services.

I hope this helps.