Twitter, Facebook, Pinterest and many other online communities ask their users to populate a location field in their user profiles. The information that is entered into this field has many uses in both industry and academia, with location field data providing valuable geographic context for operators of online communities and playing key roles in numerous research projects. However, despite the importance of location field entries, we know little about how to design location fields effectively. In this paper, we report the results of the first controlled study of the design of location fields in user profiles. After presenting a survey of location field design decisions in use across many online communities, we show that certain design decisions can lead to more granular location information or a higher percentage of users that fill out the field, but that there is a trade-off between granularity and the percent of non-empty fields. We also add context to previous work that found that location fields tend to have a high rate of non-geographic information (e.g. Location: "Justin Bieber's Heart"), showing that this result may be site-specific rather than endemic to all location fields. Finally, we provide evidence that verifying users' location field entries against a database of known-valid locations can eliminate toponym (place name) ambiguity and any non-geographic location field entries while at the same time having little effect on field population rate and granularity.