Should I warn that drop down filters are mandatory?

Question

When dealing with various drop down list of options, with one acting as a filter to another and the last one being the desired option per se, it is more advisable to treat all drop downs as obligatory or just the final one used?

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Let me set an example:

Country: [ select a country ⌄ ]
State:   [ select a state   ⌄ ]
City:    [ select a city    ⌄ ]

At first only the country drop down is loaded. As the user selects the country the state one got loaded. Finally, when the user selects a state, the city one is loaded.

Like: United States → Illinois → Chicago.

In the end what is really needed by the form is that the user is located at Chicago city.

If the user attempts to submit without selecting a state or a country, should it be warned that they are obligatory or just that the city it is (since the two first act as mere filters)?

Answer 1

In the case of city selector the better solution could be autocomplete control, which has features:

• quick city selection
• disambiguation elimination (e.g. duplicatename cities in the USA)
• removes national specificity (some countries don't have states, etc.)
• less cognitive load, as user concentrates on city entering
• unobtrusive filtering: [City → Country → State] vs [Country → State → City]

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In your current interaction (select → load) it seems impossible to skip Country and State fields. Anyway, filters look like hierarchical fields, and there are no cues of skip is allowed.

Answer 2

City is mandatory input and it depends on State and state in turn depends on Country. So, if user submits without selecting Country or State or City and there are no defaults set to these fields, system should warn that these are obligatory.

Answer 3

Adding onto @Alexey's answer, I would suggest allowing users to enter the City, State or the city's Postal Code. Once a user's focus moves away from the location form field, format the location correctly or prompt the user if more information is required. For example:

• User enters enough data, such as London, UK, and this is reformatted upon the user changing focus away from the form field to London, United Kingdom.

• User doesn't enter enough data, such as London, and then is presented with a list of possible options that they could have meant:

  • London, United Kingdom
  • London, OH, United States

In order for this to work though you'll need a pretty robust geo-data library to reference in real-time.