## Abstract
This ERC defines a storage layout convention for Solidity and other EVM languages that preserves data locality in the Binary Trie ([EIP-7864]( EIP-7864: Ethereum state using a unified binary tree )). By deriving mapping slots as `(hash(key) & ~0xFF) | base_slot`, all mappings for the same key are co-located within a single 256-slot trie page. This reduces branch openings and witness sizes when accessing multiple values associated with the same key.