GeoTIFF adds six TIFF tags. One of them is a directory of “GeoKeys”, small keyed values that describe the coordinate system, much like a second, smaller set of tags. This page follows the OGC GeoTIFF Standard 1.1 (OGC 19-008r4), read 2026-11-12, which keeps the keys of the original 1.0 specification and renames several of them.
GeoKey directory
A list of 16-bit numbers: a 4-number header, then 4 numbers per key, sorted by key ID.
| Header | Meaning |
|---|---|
| KeyDirectoryVersion | 1. |
| KeyRevision | 1. |
| MinorRevision | 0: GeoTIFF 1.0, accepted for existing files that use no codes dropped in 1.1. 1: version 1.1, recommended for writing. |
| NumberOfKeys | Entries that follow. |
| Entry | Meaning |
|---|---|
| KeyID | Which key. |
| TIFFTagLocation | 0: the value is the next number itself (one SHORT). 34736: in GeoDoubleParams. 34737: in GeoAsciiParams. 34735: further on in this directory. |
| Count | Number of values (characters for text, including the |). |
| Value_Offset | The value, or the index into the tag named. |
GeoKeys
Names in GeoTIFF 1.1, with the 1.0 name where it changed. Codes for coordinate systems, datums, ellipsoids, prime meridians and units are EPSG codes; 32767 means “user-defined”, described by the other keys; 0 means undefined.
| ID | Key | Value |
|---|---|---|
| 1024 | GTModelTypeGeoKey | 0 undefined or unknown, 1 2D projected, 2 2D geographic, 3 geocentric 3D, 32767 user-defined; 4–32766 reserved. |
| 1025 | GTRasterTypeGeoKey | 0 undefined or unknown, 1 PixelIsArea, 2 PixelIsPoint, 32767 user-defined (0 and 32767 not recommended). |
| 1026 | GTCitationGeoKey | Text. |
| 2048 | GeodeticCRSGeoKey (GeographicTypeGeoKey) | EPSG geographic CRS, such as 4326. |
| 2049 | GeodeticCitationGeoKey (GeogCitationGeoKey) | Text. |
| 2050 | GeodeticDatumGeoKey (GeogGeodeticDatumGeoKey) | EPSG datum. |
| 2051 | PrimeMeridianGeoKey (GeogPrimeMeridianGeoKey) | EPSG prime meridian. |
| 2052 | GeogLinearUnitsGeoKey | EPSG unit, such as 9001 metre. |
| 2053 | GeogLinearUnitSizeGeoKey | Metres per unit (double). |
| 2054 | GeogAngularUnitsGeoKey | EPSG unit, such as 9102 degree. |
| 2055 | GeogAngularUnitSizeGeoKey | Radians per unit. |
| 2056 | EllipsoidGeoKey (GeogEllipsoidGeoKey) | EPSG ellipsoid. |
| 2057 | EllipsoidSemiMajorAxisGeoKey | Double. |
| 2058 | EllipsoidSemiMinorAxisGeoKey | Double. |
| 2059 | EllipsoidInvFlatteningGeoKey | Double. |
| 2060 | GeogAzimuthUnitsGeoKey | EPSG angular unit for azimuths. |
| 2061 | PrimeMeridianLongitudeGeoKey (GeogPrimeMeridianLongGeoKey) | Double. |
| 3072 | ProjectedCRSGeoKey (ProjectedCSTypeGeoKey) | EPSG projected CRS, such as 32633 (UTM zone 33N). |
| 3073 | ProjectedCitationGeoKey (PCSCitationGeoKey) | Text. |
| 3074 | ProjectionGeoKey | EPSG conversion (projection with parameters). |
| 3075 | ProjMethodGeoKey (ProjCoordTransGeoKey) | Projection method. |
| 3076 | ProjLinearUnitsGeoKey | EPSG linear unit. |
| 3077 | ProjLinearUnitSizeGeoKey | Metres per unit. |
| 3078, 3079 | ProjStdParallel1GeoKey, ProjStdParallel2GeoKey | Standard parallels. |
| 3080, 3081 | ProjNatOriginLongGeoKey, ProjNatOriginLatGeoKey | Natural origin. |
| 3082, 3083 | ProjFalseEastingGeoKey, ProjFalseNorthingGeoKey | |
| 3084, 3085 | ProjFalseOriginLongGeoKey, ProjFalseOriginLatGeoKey | |
| 3086, 3087 | ProjFalseOriginEastingGeoKey, ProjFalseOriginNorthingGeoKey | |
| 3088, 3089 | ProjCenterLongGeoKey, ProjCenterLatGeoKey | Projection centre. |
| 3090, 3091 | ProjCenterEastingGeoKey, ProjCenterNorthingGeoKey | |
| 3092 | ProjScaleAtNatOriginGeoKey | Scale factor. |
| 3093 | ProjScaleAtCenterGeoKey | Scale factor. |
| 3094 | ProjAzimuthAngleGeoKey | Azimuth angle. |
| 3095 | ProjStraightVertPoleLongGeoKey | Longitude of the straight vertical pole. |
| 4096 | VerticalGeoKey (VerticalCSTypeGeoKey) | EPSG vertical CRS. |
| 4097 | VerticalCitationGeoKey | Text. |
| 4098 | VerticalDatumGeoKey | EPSG vertical datum. |
| 4099 | VerticalUnitsGeoKey | EPSG linear unit. |
Projection methods
ProjMethodGeoKey values 1–27 are GeoTIFF map projection method codes (the standard’s Annex C):
| Code | Method | Code | Method |
|---|---|---|---|
| 1 | Transverse Mercator | 15 | Polar Stereographic |
| 2 | Transverse Mercator (modified Alaska) | 16 | Oblique Stereographic |
| 3 | Oblique Mercator | 17 | Equirectangular |
| 4 | Oblique Mercator (Laborde) | 18 | Cassini–Soldner |
| 5 | Oblique Mercator (Rosenmund) | 19 | Gnomonic |
| 6 | Oblique Mercator (spherical) | 20 | Miller Cylindrical |
| 7 | Mercator | 21 | Orthographic |
| 8 | Lambert Conformal Conic (2 standard parallels) | 22 | Polyconic |
| 9 | Lambert Conformal Conic (Helmert, 1 parallel) | 23 | Robinson |
| 10 | Lambert Azimuthal Equal Area | 24 | Sinusoidal |
| 11 | Albers Equal Area | 25 | Van der Grinten |
| 12 | Azimuthal Equidistant | 26 | New Zealand Map Grid |
| 13 | Equidistant Conic | 27 | Transverse Mercator (south oriented) |
| 14 | Stereographic |