Maps have long been an important method for exploring, representing, and communicating data. This chapter provides an introduction to the principles of map design for use with online data that has geographic coordinates. First it outlines fundamental issues associated with cartographic design –classification, normalization, generalization, symbology, color – and introduces a range of map types – dot, proportional symbol, choropleth – and guidelines for their appropriate use.  This chapter then provides an overview on gathering online data and reviews data formats and a range of open source desktop and online mapping tools – QGIS, Leaflet, Mapbox – available for use. The last part of the chapter applies these principles to a case study using geosocial media data and focuses on the pitfalls associated with such sources and the benefits of a mixed methods approach to these data. Not only can online data be mapped for visual analysis, it is also useful to use a range of quantitative methods to understand relationships between different subsets of the data. In addition, small datasets, e.g., even a few dozen or hundred observations, leveraged from a larger ‘big data’ repository are valuable in allowing researchers to examine localized events or outliers to the norm.