Dear colleagues,

I needed to measure the association degree (and ideally its p-value) between
two maps, one representing richness of European bryophytes and the other
vascular plant richeness. From the maps it is clear the two patterns are
reversed: bryophytes 'rule' in the north, and vascular plant richness is
higher in  southern Europe.

I have used isodata algorithm followed by a Maximum-likelihood
classification to generate a map showing four different areas in Europe
(lowbryo-lowvasc, lowbryo-highvasc, highbryo-lowvasc, and
highbryo-highvasc). Additionally, I would like to run a correlation analysis
but corrected for the univariate spatial correlation of each variable
(bryophytes and vascular plant richness); a global correlation map-to-map is
meaningless here.

I found a statistic that would suit my needs (Lee, S.-I. 2001. Developing a
bivariate spatial association measure: An integration of Pearson's r and
Moran's I. Journal of Geographical Systems 3(4): 369-385). It is implemented
in 'The Map Comparison Kit' (http://www.riks.nl/mck/), but it return values
outside the -1 to 1 values, which makes me think there is something wrong in
the code or the statistic.

Can somebody guide me to a R package allowing me to measure the association
between these two grids?

thanks in advance,

Jesús

 

 

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Jesús Muñoz PhD            e-mail: jmunoz@rjb.csic.es

Real Jardín Botánico (CSIC)

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