A knowledge graph is a network that interconnects concepts, objects, or events according to domain specific relationships and terminology. Spatial knowledge graphs model locations and how they are spatially related to each other according to semantic properties and are useful for helping to automate the integration of geographic data across silos. Information systems used to make decisions often have different pictures of the geographies (i.e. people, places, and infrastructures) they respectively cover. Within a single area, different programs collect and store different geographic data in siloed systems at different times, leading to discrepancies and duplication of effort. This also results in decisions based on incomplete and out-of-date geographic data (e.g., spatial distribution of population and resources). GeoPrism Registry is an open-source Common Geo-Registry (CGR) implementation that utilizes spatial knowledge graphs to provide a single source of truth for managing geographic data over time across multiple information systems and data sources. It is used to publish, access, and manage changes over time to hierarchies and geospatial data for geographic objects such as administrative divisions, infrastructure and other relevant physical features. GeoPrism Registry uses geo-ontologies to define semantic properties and relationships that implement spatial knowledge graphs using a graph database. Changes to attribute values, relationships, and geographies are managed for different time periods. Historical views of data can be generated for any time period. The application has been released under the Lesser General Public License (LGPL) and was developed using only open-source components including OpenJDK, MapboxGL, PostgreSQL, OrientDB, Solr, GDAL, and GeoServer. This talk will demonstrate how spatial knowledge graphs defined in GeoPrism Registry using FOSS4G tools can: 1. contextualize data from different sources in both time and space, 2. use geographic objects as the common link between data sources, 3. facilitate trend analysis, and 4. aggregate data according to different hierarchies Support for the development of GeoPrism Registry was provided by the Bill and Melinda Gates Foundation via the Digital Solutions for Malaria Elimination (DSME) Project and the DSME Community. The DSME project uses geo-enabled information systems to improve the efficiency and effectiveness of malaria surveillance, program planning, and intervention.