| o | ostwarts |
| O | Osten = east |
| OAB | Operational advisory broadcasts |
| OAC | Osterreichischer Automobil Club |
| OACH | Office of the Assistant Chief Hydrologist |
| OADCES | On-line Aerotriangulation Data Collection and Editing System |
| OAdW | Osterreichische Akademie der Wissenschaften |
| OAMTC | Osterreichischer Automobil-, Motorrad- und Touring-Club |
| OAS | Orbit Adjustment Subsystem; Organization of American States |
| OASIS | Oceanic and Atmospheric Scientific Information System |
| Obj. | Objekt |
| OBM | Ontario Basic Mapping Program |
| OBRP | Object representation |
| OBS | Office of Biological Services |
| OCAP | Ohio Capability Analysis Project |
| OCE | Office of the Chief of Engineers |
| OCH | Office of the Chief Hydrologist |
| OCL | Object Constraint Language |
| OCLC | Ohio College Library Center |
| OCR | Optical Character Recognition; Optical Character Reader |
| OCRS | Ontario Centre for Remote Sensing |
| OCS | Office of Cadastral Survey (BLM); Operational Control System; Outer Continental Shelf; Ocean Color Scanner |
| OCTS | Ocean Color and Temperature Scanner |
| OCX | Object Component eXtension |
| OD | Optical disc; Outside diameter |
| ODBC | Operational Database Connectivity |
| ODE | Open development environment |
| ODF | Oregon Dept. of Forestry |
| ODFW | Oregon Dept. of Fish and Wildlife |
| ODGMI | Oregon State Dept. of Minerals and Mineral Industries |
| ODGS | Ohio Div. of Geological Survey |
| ODNR | Ohio Dept. of Natural Resources |
| ODOP | Ohio Digital Orthophotography Project |
| ODOT | Ohio Dept. of Transportation |
| OEEPE | Organisation europeene d'etudes en photogrammetrie experimentale |
| OESA | Office of Earth Science Applications |
| OF | Open file; Open-file |
| Offn. | Offnung = aperture, opening |
| OFIPLAN | Oficina de Planificacion Nacional (Costa Rica) |
| OFR | Open file report; Open-file report |
| OFSS | Open-file Services Section |
| OGC | Open GIS Consortium, Inc. |
| OGDI | Open Geospatial Datastore Interface |
| OGIS | Open GIS |
| OGRIP | Ohio Geographically Referenced Information Program |
| OGS | Ontario Geological Survey; Oklahoma Geological Survey |
| OGW | Office of Ground Water |
| OGWP | Office of Ground Water Protection (EPA) |
| OH | Ohio |
| OHW | Office of Hazardous Wastes Hydrology |
| OIA | Office of International Activities |
| OIG | Office of International Geology |
| OIH | Office of International Hydrology |
| OII | European Commission's Open Information Interchange |
| OILT | Oil tank farm |
| OK | Okonomisk kart (Norway); Osterreichische Karte; Oklahoma |
| OKAGE | Oklahoma Alliance for Geographic Education |
| OLAP | Online analytical processing |
| OLE | Object Linking/Embedding |
| OLS | Operational Line Scan (imaging system); Ordinary Least Squares |
| OMG | Open Management Group |
| OMNR | Ontario Ministry of Natural Resources |
| OMO | Other mapping organization |
| OMTC | Ontario Ministry of Transportation and Communications |
| ON | Original negative |
| ONC | Operational Navigation Chart |
| ONERN | Oficina Nacional de Evaluacion de Recursos Naturales (Peru) |
| ONIG | Office Nationale de la Geologie (Algeria) |
| ONPR | Office of National Petroleum Reserve (USGS) |
| OO | Object-Orientation |
| OOPEC | Office for Official Publications of the European Communities |
| OOSI | Osterreichisches Ost- und Sudosteuropa-Institut |
| OPAC | Online public access catalog; online patron access catalog |
| OPCS | Office of Population Censuses and Surveys (U.K.) |
| OPEC | Organization of Petroleum Exporting Countries |
| OPEDS | Outside Plant Engineering Design System (ESRI, Bell South) |
| OPL | Oilfield Publications |
| OPP | Operational Positional Procedure |
| OPR | Office of Planning and Research |
| OPS | Optical sensor(s) |
| OPUS | Online Positioning User Service (US NGS) |
| OR | Oregon |
| OQ | Orthophoto quadrangle |
| ORBIMAGE | Orbital Imaging Corp. |
| Ore. | Oregon |
| ORH | Office of the Regional Hydrologist |
| ORID | Ortho Rectified Image Data |
| ORRH | Office of the Regional Research Hydrologist |
| ORSER | Office for Remote Sensing of Earth Resources (Penn. State Univ.) |
| ORSTOM | Office de la Recherche Scientifique et Technique Outre Mer |
| OS | Ordnance Survey (U.K.); Object space; Operating System |
| OSCAR | Online Satellite Catalog and Request System (NOAA) |
| OSD | Overseas Surveys Directorate (U.K.); Office of the Secretary of Defense (U.S.); On-screen display |
| OSDA | Oregon State Dept. of Agriculture |
| OSEC | Ocean Systems Engineering Corp. |
| OSECO | Ogden Surveying Equipment Company |
| OSEDA | Office of Social and Economic Data Analysis (Missouri) |
| OSFD | Oregon State Forestry Dept. |
| OSGB | Ordnance Survey (U.K.) |
| OSI | Open Systems Interconnect model; Open Systems Interconnection |
| OSIP | Operational Satellite Improvement Program |
| OSLS | Oklahoma Society of Land Surveyors |
| OSM | Office of Surface Mining |
| OSNI | Ordnance Survey of Northern Ireland |
| OSOA | Optimal Statistical Objective Analysis |
| OSP | Office of State Planning |
| OSPE | Ohio Society of Professional Engineers |
| OSS | Office of Strategic Services (U.S.) |
| OSSI | Optronic Sensor for Stereo Imagery |
| OSTA | Office of Space and Terrestrial Applications (NASA) |
| OSTF | Ordnance Survey Transfer Format |
| OSTZ | Osterreichisches Statistisches Zentralamt |
| OSU | Oregon State University |
| OSW | Office of Saline Water; Office of Surface Water |
| OTA | Office of Technology Assessment |
| OTC | Over-the-counter; Office for Topography and Cartography (Tunisia) |
| OTF | On-the-fly |
| OTH | Over the horizon |
| OTHT | Over the horizon targeting |
| O.U. | Open under |
| OUCLS | Ontario Universities' Library Cooperative System |
| OUO | Official use only |
| OVN | Optical visible near-infrared |
| OW | Oil well |
| OWDC | Office of Water Data Coordination |
| OWRD | Oregon Water Resources Dept. |
| OWRR | Office of Water Resources and Research |
| OWRT | Office of Water Research and Technology |