This function requires an environment variable to be set for MAPQUEST_API_KEY
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Sign up for free for the API-key at https://developer.mapquest.com/plan_purchase/steps/business_edition/business_edition_free/register
Add your MAPQUEST_API_KEY to your .Renviron using file.edit('~/.Renviron')
Then add a line for MAPQUEST_API_KEY=<yourkey> Then run readRenviron('~/.Renviron') to load this environment variable into your session.
This entitles you to use 15 000 free transactions per month.
Either use the street, zip, city and country parameters (all of them), or use only the location parameter.