joining tables or measures

Let's see if this works for you.

First create dimension tables for Stores and Cities. The model looks like this:

And it creates the following measures:

For the number of physical stores

Tiendas Físicas = 
DISTINCTCOUNT('Listado de Tiendas'[Ciudad])

For the number of cities with presences

Ciudades con Ventas = 
DISTINCTCOUNT('Ventas'[Ciudad])

And for the total calculation

Total =
VAR FT =
    VALUES ( 'Listado de Tiendas'[Ciudad] )
VAR CV =
    VALUES ( Ventas[Ciudad] )
RETURN
    COUNTROWS ( DISTINCT ( UNION ( FT, CV ) ) )

I attach the sample PBIX file