Being a dungeon master takes a lot of work. You have to build a whole world and create a story that is cohesive, but flexible enough to allow the players to do their own thing. It involves creating an array of characters with whom the players can interact, organizing challenging encounters, setting traps, and creating puzzles.
As if that’s not enough, you need to have maps for the various locations that the adventurers visit. Now, some situations can get away with a “theater of the mind” approach. This is, after all, a role playing game. Characters can visit a market or a throne room to talk to the king without needing to lay down tiles for conversation.
Some times, though, you need to have a map of the terrain laid out in front of you. This is true for dungeon crawls, as specific squares may be trapped and the positioning of party members is crucial.
It also comes into play when the party gets into a fight. Inside or outside, you need to know what you’re facing and where they are in relation to you. This is especially essential as positioning yourself in the right way can yield benefits, such as a bonus to your attack roll.
While some players use white boards that can be drawn on, Wizards of the Coast decided to do dungeon masters a favor and release a series of kits that featured pre-made map tiles. The Essentials line released a box set for the wilderness and the city, though there are other box sets floating around as well.

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The “Wilderness” box set says that it features 10 double sided tiles. This is true, though most of the tiles snap apart into several smaller pieces. This is something of a boon, though, as it gives the dungeon master at least a little bit more variety. This way, they can place the pieces where they need to go and even reuse them in different layouts for multiple encounters.
Having only 10 pieces helps keep the price down, but it does seem like they could have put a couple more tiles in the box with no problem.

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Interestingly enough, the box itself (or the lid to be more specific) seems to act as a tile (though, no, thankfully, it is not counted as one of the 10.) I’m not sure if it’s meant to actually be used or if they did it for aesthetic purposes.
I suppose you could if you wanted to, the terrain’s open enough. However, with only an 8 by 10 grid, a 5 person party fighting 5 monsters would leave little room for mobility. It isn’t like you could set this down among other tiles either, as the lid ends up being much higher than anything that would be laid down around it.
I’d be interested to see what dungeon masters do with that. I can’t think of any other reason to style the box that way, but having a DM just put the lid down on the table before combat seems like it would be really strange.

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I said before that the multiple smaller tiles offers the dungeon master more variety. In some ways, this is true. At the same time, though, a lot of the pieces feel redundant.
I’m not sure we needed multiple tiles dedicated to fires. Water is also another thing that eats up a lot of tiles. And rocks, there are a lot of tiles dedicated to rocks.
You’d think that the tiles being double sided would help alleviate this somewhat, but the tiles go quick.
I know, this is the wilderness and those are all things you’d find, but an inordinate amount of squares are dedicated to them when you’d think that you’d want the characters to have places to go in order to do things.

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I was surprised at how few “open terrain” tiles there were. You’d think that those would be the dominantly featured option, but really, it seems like there are only a handful.
You could argue that having things in the way makes combat more interesting, but I’d think that’s what the smaller tiles would be for.
Some of the locales featured are OK. There are various ruins, and even some sort of remote cabin; but it seems like a DM can only use them once, barring the party returning to the location for whatever reason.

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I think the smaller pieces are the most useful. Not only is there more variety in terms of the tiles themselves, but the dungeon master is able to shuffle them around to a much greater extent.
Something like a cart or a campfire tile can be used again and again with no eyebrows raised, but trying to make an already used larger tile seem new by rotating it doesn’t work quite as well.