I want to join the results of sDNA analysis to urban blocks and I have a list of questions 1- Do I need to weight sDNA values of the street segments (i.e. the links) before spatial join to urban blocks layer? 2- if so, what is the formula for the weighting variable? 3- How could I aggregate the sDNA values of surrounding segments of each block? 4- and lastely, could anybody in simple language illustrate the difference between betweenness and two phase betweenness and when should I depend on the two phase betweennness?
Questions 1-3 are not really an sDNA question, but a question of how to report street level centrality statistics for blocks. My instinct would be to go for a length weighted mean. If your GIS join functions can't do this automatically, then compute
length * (statistic of interest) for each link, then after joining links to blocks, for each block compute
SUM(statistic of interest)/SUM(length).
Question 4. I think two phase betweenness is the more intuitive one to understand - it models a fixed quantity of something at an origin which is distributed over all available destinations. In ordinary betweenness, by contrast, the proximity of origins to destinations generates extra activity - the quantity of activity for each origin is not fixed, but depends on how many destinations there are to interact with.