How do I increase the number of ore boulders on surface?

With a custom planet, how do I increase the number of ore boulders on surface?

 

In the EnvironmentItems part of the planet's definition, items are placed by biome and voxel material they're on top of. The quantity of items are determined by the density. Here's a quick cover of the basics of the EnvironmentItems.

Here's an example from the standard earth-like:

<Item>
<Biomes>
<Biome>85</Biome> Biome number is the color in the green channel of the (what ever side)_mat.png file
</Biomes>
<Materials>
<Material>Woods_grass</Material> This specifies which voxel material the items will spawn on from VoxelMaterials_planetary.sbc
</Materials>
<Items>
<Item TypeId="MyObjectBuilder_VoxelMapStorageDefinition" GroupId="StoneCoverageIronCore" ModifierId="EarthForestArea" Density="0.002" />
This is the specific item. This references voxel shapes in the VoxelMapStorages.sbc file by the GroupID. The modifier is from the VoxelMaterialChanges.sbc. The Density is how frequently they appear.
</Items>
<Rule>
<Height Min="0" Max="0.7"/> How high the terrain the item will spawn
<Latitude Min="0" Max="80"/> Range of degrees from equator the item will spawn
<Slope Min="0" Max="10"/> Range of degrees of slope the item will spawn
</Rule>
</Item>

 

Thank you. I'll look into this tomorrow.