| Label | Concept definition | Figure(s) | Code |
|---|---|---|---|
| UNCONTROLLED_AIRSPACE | Any <AIRSPACE> in which air traffic control service is not available; uncontrolled airspace. | 1297 | |
| UNDERGROUND_BUNKER | A <BUNKER> that is used as a command and control centre or for encampment; underground bunker. | 1298 | |
| UNDERGROUND_DWELLING | A <DWELLING> under the <TERRAIN>; underground dwelling. | 1299 | |
| UNDERGROUND_RAILWAY | A <TUNNEL> under the <TERRAIN> through which a metropolitan electric <RAILWAY> travels; underground railway. | 1300 | |
| UNDERGROUND_STRUCTURE | An underground <STRUCTURE>, such as a <BUNKER> or underground <PARKING_GARAGE>. | 1477 | |
| UNDERGROUND_WATER | <WATER> situated under the <TERRAIN> but reachable by <WELL>s; underground water. Underground water is also known as phreatic water. | 1301 | |
| UNDERMINED_LAND | A <TRACT> that was previously undermined through mining activities and that either has already partly subsided and/or that is in the process of subsiding; undermined land. | 1302 | |
| UNDERWATER_COMMUNICATION- _DEVICE |
A <DEVICE> located in a <WATERBODY> and used to provide two-way communication; underwater communication device. EXAMPLE <ACOUSTIC_TRANSDUCER>. |
1303 | |
| UNDERWATER_HAZARD | An <UNDERWATER_OBJECT> known to be hazardous to navigation on <WATERBODY_SURFACE>s; underwater hazard. | 1304 | |
| UNDERWATER_OBJECT | An <OBJECT> under a <WATERBODY_SURFACE>. EXAMPLE <MARINE_WRECK>. |
1305 | |
| UNDERWATER_REGION | A <REGION> under a <WATERBODY_SURFACE>. | 1306 | |
| UNMANNED_WINGED_AIRCRAFT | A winged <AIRCRAFT> operating without a pilot onboard; unmanned winged aircraft. | 1307 | |
| UNMONUMENTED_POINT | A formally recognized survey or reference <LOCATION> that is not represented by a physical <BOUNDARY_MONUMENT> and/or <BENCHMARK>; unmonumented point. | 1308 | |
| UNVEGETATED_LAND | A <TRACT> with little (less than 5 percent) or no <VEGETATION>; unvegetated land. | 1309 | |
| URANUS | The primary <PLANET> of the <SUN> that is seventh in distance from the <SUN>, with an orbital mean <<RADIUS>> of approximately 2 875,0 million kilometres; Uranus. | 1310 | |
| UTILITY_HELICOPTER | A <HELICOPTER> designed or designated for various utility operations. | 1311 | |
| UTILITY_VESSEL | A <WATER_SURFACE_VESSEL> designed or designated for various utility operations. | 1312 | |
| UTILITY_WINGED_AIRCRAFT | A winged <AIRCRAFT> designed or designated for utility, non-transport purposes. | 1313 |
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