How can ethnographic research improve surveys? I illustrate the benefit of sustained qualitative research on survey design and implementation with reference to my own study of a neglected urban population: internal migrants. Such migrants are an important part of expanding South Asian and African cities. The informality and circular mobility of these populations prevent researchers from accessing them through traditional residence-based surveys. Scant existing knowledge weakens our ability to design theoretically precise and contextually appropriate survey instruments for these understudied communities, particularly cognitively demanding survey experiments to assess political attitudes. I argue that ethnographic fieldwork can help researchers address insufficient access and weak ecological and construct validity. I substantiate these arguments with data and insights from 15 months of fieldwork among circular urban migrants in India. First, I show how ethnography can help design context-sensitive sampling strategies that mitigate concerns of inadequate coverage, high non-response, and inefficiency. Second, I show how ethnography can be used to improve the ecological and construct validity of survey-based experiments. Finally, I show how such ethnographic innovations can be applied beyond the study population that inspired them. Sustained qualitative fieldwork can thus improve survey-based research on political behavior on neglected communities across the global south.