by ftl_ftw
Spoilers only for the initial board/cards:[o]
Route leaving the city: Each city with a recon has a line leaving it. It's actually easy to miss because it looks like it's just connecting the "recon" box to the city, but it's drawn to look like a route leading off to an unknown area.
Cards matching those: each recon box has icons for cards you need to discard there (all at once). The cards you need are also described in text. The ones visible on the board are:
Washington - Recon with 3 blue cards. (For example, you could discard London, London, New York.)
Sao Paolo - Recon with 4 yellow cards. (For example, you could discard Lagos, Sao Paolo, Jacksonville, Jacksonville).
London - Recon with 4 *different* blue cards. (For example, you could discard London, Washington, New York, and one other blue city card besides those three. You could not do it with just the city cards available in the prologue.)
Cairo - Recon with 4 *different* black cards. (For example, you could discard Istanbul, Cairo, Tripoli, and one other black city card besides those. You could not do it with just the city cards available in the prologue.)
Lagos - Recon with 5 *different* yellow cards. (For example, you could discard Lagos, Sao Paolo, Jacksonville, and two other yellow city cards beside those. You could not do it with just the city cards available in the prologue.)
[/o]