One catchment for every market is a simplification. A large out-of-town store draws from much further than a convenience shop on a high street, and a market in open countryside stretches further than one in a dense city. Asymmetric catchments let you say so.

On the Scenarios page, under Define catchment areas, switch Size from Symmetric to Asymmetric. The Asymmetric catchments window opens, and the pane then shows the range you've set, with a pencil to come back to it.

The catchment belongs to the market, not to the competitors in it: it's the size of the ring drawn around the site the market is centred on. Everything that falls inside it still counts.

By category

The quicker route. Choose a column to group by - fascia, store format, size band, urbanicity - and set one catchment for each value in it. Tick the rows, type a catchment, and Assign applies it to all of them.

So a scenario might give the superstore operator 2km and the convenience chain 1km, and be done in two assignments.

By market

The precise route: every market listed on its own, with the site it's centred on and the fascia that owns it. Filter the list to find the ones you want, tick them, and assign. Use it for the handful of markets that don't fit the pattern - the one rural store, the market where you know the local evidence.

Assigning works the same way as the category tab, in bulk. Tick the markets you want - the box in the header row takes the lot - then type the catchment under Catchment value on the right. The button tells you how many markets it will apply to.

Click Assign and every ticked market gets that catchment in one go, so a filtered list of ten rural stores takes one assignment, not ten.

The counter at the bottom - 0/35 completed - tracks how many markets still have no catchment, and the pane shows the same thing in red. Every market needs one before the analysis will run; Reset all clears them and starts again.

Click Update to apply, then run the analysis as usual. Each market's card and the table show the catchment it was given, so there's no guessing later about which market got what.

Pro tips

• Set the pattern by category first, then override the exceptions by market. Doing it the other way round means typing 35 numbers.

• Wider catchments mean more overlaps. Expect the market count to climb, and compare against a symmetric run so you can say what the wider catchment actually changed.

• Save a symmetric scenario and an asymmetric one separately. "Same deal, two views of the geography" is a far better answer than one you re-ran.

• The limits for each catchment type are the same as for symmetric ones - see how to define catchment area in Sloc Local.