Interesting video! Unfortunately I don`t know the Angular - I am learning the React in near future. Why you don`t load a list of cities for given state from the server in frontend? A list of all the cities and towns in the USA may be too large. But for the one given state (of the USA) you may use a clue - when a user typing letters , the browsr matching content of with this list and show avaliable variants. So you can choose by mouse (touching in a phone) the correct variant from list or typing manually . Sending each request (for validation) witn city name to the server takes time may annoy user of your web application. For this purpose you can use the "input" event and attaching dynamic list menu with cities , that has been matched with content of the HTML element
