How does the distribution of ores & chests change with world size?

In small worlds, resources are closer together.

In large worlds, resources are farther apart.

According to the Terraria wiki page on World Size,

It also seems that in larger worlds, resources are much farther apart from each other in comparison to the smaller ones. This means that in smaller worlds, resources are much easier to locate and mine

This can be seen by using MoreTerra to display the whole map. Taking same-scale slices of each world size reveals the sparser dispersions of rare resources in the larger maps.

For a numerical argument, you could count the number of rare resources on n small worlds, n medium worlds and n large worlds. Then divide each count by the respective world dimenions and average the numbers. This method will give the average density of resources on each map size. The greater n is, the more accurately average resource density is estimated.

For example, below are three same-scale slices of each world size. Note, this is only one sample, so the total counts do not accurately represent the average resource density of each map size.

Small World

^{4300 x 1200 blocks}

• ^{Altar - 9}
• ^{Chest - 3}
• ^{Heart Stone - 4}
• ^{Shadow Orb - 5}
• ^{Amethyst - 16}
• ^{Diamond - 3}
• ^{Emerald - 9}
• ^{Ruby - 4}
• ^{Sapphire - 12}
• ^{Topaz - 16}
• ^{Total - 81}

Medium World

^{6300 x 1800 blocks}

• ^{Altar - 6}
• ^{Chest - 3}
• ^{Heart Stone - 2}
• ^{Shadow Orb - 7}
• ^{Amethyst - 5}
• ^{Diamond - 0}
• ^{Emerald - 1}
• ^{Ruby - 1}
• ^{Sapphire - 2}
• ^{Topaz - 5}
• ^{Total - 32}

Large World

^{8400 x 2400 blocks}

• ^{Altar - 2}
• ^{Chest - 0}
• ^{Heart Stone - 3}
• ^{Shadow Orb - 9}
• ^{Amethyst - 2}
• ^{Diamond - 1}
• ^{Emerald - 1}
• ^{Ruby - 1}
• ^{Sapphire - 4}
• ^{Topaz - 2}
• ^{Total - 25}

Symbol legend

Another way to find the exact dispersion ratio is to look at the code.

In response to people asking about an open source version of Terraria, Redigit says,

This will probably happen eventually, but the decision to not obfuscate Terraria was made for a reason

So until the open source code is released, somebody could dig through the decompiled code and find the variables that control the base resource density of each map size.

The larger the world the more likely you are to find golden chests, floating islands, and more loot in the dungeon. Although there is more loot the progress becomes a lot slower in larger worlds than in smaller worlds because of the fact that there is more to explore. If you are a complete beginner at Terraria than i suggest you choose small world, but if you already know what you want to do than choose large at your own expense. If you want to get ores easier than small. If you want to get a lot of ores than large. Medium isn't really a type that is chosen that much because It's sort of in between, I don't like it because it just messes with my head(the dimensions). If you are looking for more(quantity) chances of finding rare golden chests/locked shadow chests than choose large. In the shadow world they spawn with a huge number. In some cases yes, resources can be a lot closer in a smaller world but more rare.

Above is an overview of a small world, as you can see, small dungeon, 3 floating islands, 2 small corruptions, a jungle, small deserts.

Above, a Large world, the image is a very small so i will post a link where i found the image, if you can see the picture, there are 5-6 floating islands, 3 different corruption areas, a jungle, a bigger dungeon and A LOT more space to explore. You can also easily tell that the large world is deeper and higher so you can easily make harpy farms and explore more caves before reaching the underworld.

Large World