GIS mapping software (GIS - Geographical Information System) can be expensive and difficult to use. What we want is a simple cost effect GIS mapping product.
I have found that using a product like Tableau you can quickly and cost effectively create simple GIS mapping solutions.
All you need is to find the longitude and latitude of the locations of you interest. Using a pivot table approach all you then need is to put the longitude values on the rows and latitude on the columns and a map appears with your locations shown.
On the internet you can find websites that can translate postal codes or zip codes to longitude and latitude.
Additional information can then be added to the map to show demographics. e.g. sales value, size of operation etc
Here are a few examples: