SpatialML is an annotation scheme for marking up references to places in natural language. It covers both named and nominal references to places, grounding them where possible with geo-coordinates, including both relative and absolute locations, and characterizes relationships among places in terms of a region calculus. A freely available annotation editor has been developed for SpatialML, along with three annotated corpora, including a corpus of annotated documents released by the Linguistic Data Consortium. Inter-annotator agreement on SpatialML extents is 77.0 F-measure on that corpus, but 92.3 F-measure on another (ProMED) corpus. The paper discusses a number of issues affecting inter-annotator agreement.