diff --git a/hapi-dev/HAPI-data-access-spec-dev.md b/hapi-dev/HAPI-data-access-spec-dev.md
index e98f54b..31e5eb6 100644
--- a/hapi-dev/HAPI-data-access-spec-dev.md
+++ b/hapi-dev/HAPI-data-access-spec-dev.md
@@ -864,6 +864,7 @@ Possible component names are constrained to be one of the following:
 | `colatitude`   | Angle relative to +z axis, from 0 to 180°, or 0 to π |
 | `longitude`           | Angle relative to +x axis of a projection of the vector into the x-y plane, from -180° to 180°, or -π to π (90° corresponds to +y axis; this is also known as "East longitude") |
 | `longitude0`          | Angle relative to +x axis of a projection of the vector into the x-y plane, from 0° to 360°, or 0 to 2π (270° corresponds to -y axis; this is also known as "East longitude") |
+| `altitude`      | Altitude above a reference sphere or surface as identified in `coordinateSystemName`. For example, Earth locations are often descriped with longitude, latitude, and altitude.|
 | `other`             | Any parameter element that cannot be described by a name in this list |
 
 Many angular quantities in datasets have different names than the ones here