When I tap the map (by map I mean the map the character walks on - the ground), it glows a bit.
What happens when I click the map? Is it just an visual effect or does it cause anything else?
The visual effect is what we refer to in the industry as "feedback". It is a way of confirming input, where other elements in play may not.
If you tap on an object such as a pokémon or a pokéstop, and you see that effect, it means that the game has not registered your input on an object. Instead, it has interpreted your tap as being on vacant ground.
Apart from that, the effect has no other function.
I personally think it helps you find hidden pokies. I haven't tested it out enough to say for sure, but when green grass rustles near me, I tapped around it (it was right outside my circle) and a Nidorian appeared down the stream a bit, pretty far outside my circle. The game froze when I caught him, and when I restarted it he grass was back, I tapped in the same spot, and he appeared again. I tried it down the street, and 2 more appeared (but that could have been a coincidence of some randomly appearing). I'm going to keep trying I case I'm on to something.
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