Spatial is Not Special – Modifiable Area Unit Problem (MAUP)

I wrote a paper in 2006 about using SQL for the Modifiable Area Unit Problem (MAUP).  The example was an agricultural experiment field, and I showed how SQL could be used to calculate the descriptive statistics rather easily, and we also used SQL to develp a trend surface map to better understand the underlying trends of the data and determine the best areal units to use for grouping the data.  So, we thought we would use that example in the book.  MAUP is a conundrum that geographers have been thinking about for a long time, and quite frankly we will think about in the future.  I won’t go into what MAUP is here, for that you can buy the book!  But, one of our figures showed the data for 3 different blocking patterns and the corresponding descriptive statistics:

maup

The key is to develop descriptive statistics for each point that is located within each block.  This is easily accomplished through the CONTAINS and the GROUP BY clauses as follows:

SELECT avg(AVG_P) AS AVG_P, avg(AVG_K) AS AVG_K, var(AVG_K) AS VAR_K, var(AVG_P) AS VAR_P
FROM
(
   SELECT grid.id, avg(p) AVG_P, avg(k) AVG_K
   FROM grid, samples
   WHERE contains(grid.id,samples.id)
  GROUP BY grid.id
)

The subquery within the parenthesis computes the average Phosphorous (P) and Potassium (K) values for the soils, and groups it by the grid the points are contained in.  Based on our figure above, that means we will have 6 values for K and P.  If you wanted to leave it at that, you could put those values into a scatter plot to view the correlation, or wrap or copy the data to Excel and compute the correlation coefficient.  But, for us, we will take the 6 results from the sub query and compute the averages and variances of P and K for the overall grouped data.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s