Most of key mappings are defined according to the mnemonic priciples from spacemacs.

Using :verbose to take a closer look at a defined key map, e.g., :verbose nmap <Leader>bh:

:verbose nmap <Leader>bh
n  <Space>bh   * :Startify<CR>
        Last set from ~/.space-vim/layers/+distributions/better-defaults/keybindings.vim

When ‘verbose’ is non-zero, listing the value of a Vim option or a key map or an abbreviation or a user-defined function or a command or a highlight group or an autocommand will also display where it was last defined. If it was defined manually then there will be no “Last set” message. When it was defined while executing a function, user command or autocommand, the script in which it was defined is reported. See :h verbose-cmd.