Or even better, your supply vs. route demand.
The route demand ist variable. If you open the route page, the pax demand is calculated every time. This takes time and serverload. Imagine you ask for all routes from SFO to destinations in North America and this calculations have to be done for all the airports at the same time.
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Like Sami indicated, only querys to the database can be shown here (they need much less time and serverload). "Route is flown/ not flown by you", "aircraft type" or maybe "number of seats offered by you" woulde be querys. Of course, the more querys have to be done, the longer it takes time to load. But the calculations are the critical points).
But, even if this information woulde be shown, it dosen´t help that much. It might lead on the rong way as well. Imagine a route is announced as "already flown" with a "B737" and "140seats". Perfect. Really?
What if this route has a demand of~2.000pax/d?! My suggestion: Possibility to flag routes
Imagine you might mark route with flags in different colours on the "open new route" page. Which colour you choose for what is up to you, so everybody can develop his own sheme.
*green flag: there is free demand on the route
*red flag: demand is already filled
* blue flag: demand fits for my fleet type xyz
*orange flag: never open this route again because it has only zero demand!!
This means: you only have to go through the list once, mark the routes with flags and the next time you open the list you just have to follow your flags.
Of course, you may re-flag routes for example from green to red when you filled the demand etc.
By the way: flagging might also helpful in other list overviews in aws.
The first that comes to my mind is the used aircraft list. It would be very helpful if you can flag a specific plane. This could prevent you to click again and again on the B737 with the expired D check in the used market list. Or you could flag acceptable planes that you might acquire at a later point.