You are right that "inform" mainly means to give someone facts or information. Your example extends that sense of "inform" to the products or decisions of the user-interface designer who is informed of some facts.
In the example, "inform" means to make the design decisions reflect the fact that "searching travel routes" is the most important task. In other words, the design of the user interface reflects that information about how the users will operate the program. In still other words, if the the user-interface designer is informed of that fact about "searching travel routes", the user-interface design can make a better-informed decision about where to put "search route" in the screen.
The same way of extending a word's primary sense, describing something mental, to the products of a person's mind, occurs frequently in English. Here are a few examples:
A "smart decision" is a decision made by a smart person, or at least a person who was able to decide in the same manner as a smart person.
A "confused screen layout" suggests both that the elements of the screen layout are run together in a mess, and that the user-interface designer was confused when designing it.
An "informed choice" is a choice made by someone who has examined the available alternatives and learned good information about their pros and cons.
A "stupid move" in chess is a move that demonstrates little thought or insight; it appears that a stupid person made the move. Smart people sometimes make stupid moves, but you can see how the word "stupid" transfers from a person's mind to an action that results from thinking.