Creating Dependant Text field in Customizer with Checkbox

In your second line you try to get the array of all mods with:

$tsum_options = get_theme_mod( 'tsum_options');

This will always return unset, because if you want all mods you need (note the plural):

$tsum_options = get_theme_mods( 'tsum_options');

Alternatively you could immediately check the relevant mod with

$tsum_option = get_theme_mod( 'tsum_options[show_map]');