Difference maps from selection frequency maps in Marxan with Zones.

In Marxan with Zones, creating difference maps (maps that show the differences between solutions) can be complicated. These are usually created using the selection frequency maps of different scenarios, and usually using thresholding processes for categorisation purposes.

Take the following example from Venier et al. 2021. They used different thresholds of their selection frequency maps from two different scenarios to make categories which could be used to depict the differences between them. For example, mostly biodiversity (dark green), represents when the selection frequency from the biodiversity scenario was ≥70%; frequently biodiversity (light green), represents when the selection frequency from the biodiversity scenario was between 50% and 70%; Mostly aquaculture (dark blue), represents when the selection frequency from the aquaculture scenario was ≥ 70%; Frequently aquaculture (light blue), represents when the selection frequency from the aquaculture scenario was between 50% and 70%; Mostly multi-use (dark grey), represents when the selection frequency from the multi-use scenario was≥ 70%; Frequently multi-uses (light grey), when represents when the selection frequency from the multi-use scenario was between 50% and 70%; Flexible (white), represents when the difference among the three zones is less than 15%.

Using another example from Grantham et al. 2013 , the selection frequency was used to classify each planning unit into ‘mostly no-take’ (selection frequency=60–100% for no-take zone), ‘mostly sustainable fishing’ (selection frequency=60–100% for sustainable fishing zone), ‘mostly unallocated’ (selection frequency=60–100% for unallocated zone), and ‘flexible’ (the rest of the planning units selected). Letters indicate different areas within the study region (a) West Waigeo MPA, (b) Mayalibit Bay MPA, (c) Ayau-Asia MPA northern section, (d), Dampier Straits MPA, (e) Ayau-Asia MPA south section, (f) Kofiau and Boo Islands MPA and (g) Southeast Misool MPA.

These thresholds are relatively arbitrary, and will depend on the preferences of the user.