Hello Jeffrey,
Thank you a lot for your reply.
But is it necessary first to remove or account for trend in the data and then deal with spatial autocorrelation, since I plan to include spatial effects in covariates by using spatial lag regression? If I plan to include in regression equation coordinates as covariates (in order to adjust for existing trend), but I expect, for example, to have quadratic trend, then I will have to include also x sqaured and y squared as variables, right? What if I get p-values for x squared and y high (so that I have to exclude them) and thus only able to keep y squared and x. What kind of trend is there in my data in that case? Or I do not have to focus on that too much, but just include those forms of coordinate variables (along with outer independent variables) that appear significant in my regression?