Arguments

layerId  (integer)  'handle' identifier of the 'GIS Layer' to add the 'GIS Attribute' to
attDef  (list AttributeName AttributeType AttributeValue)  the AttributeDefinition list :

  AttributeName  (string)  the name of the Attribute
  AttributeType  (integer)  the type of the Attribute (see the Type Constants enumeration "Civil GIS Attribute Type")
  AttributeValue  (string or integer or double)  the initial value to be assigned : string or integer or double

Return

T on success, or NIL

Example

(vl-load-gis)  T
(setq layers (gis:get-layers))  ("shp_3857_point_2d_utf8")
(setq name (car layers))  "shp_3857_point_2d_utf8"
(setq layerId (gis:get-layer name))  1736947670764

(setq attributes (gis:layer-get-attributes layerId))  ("id" "name" "int_number" "dec_number" "date")
(gis:layer-has-attribute layerId "NewId")  NIL

(gis:layer-add-attribute layerId (list "NewId" 3 "---empty---"))  T

(setq attributes (gis:layer-get-attributes layerId))  ("id" "name" "int_number" "dec_number" "date" "NewId")
(gis:layer-has-attribute layerId "NewId")  T

Remarks

for the for the  'GIS Attribute Type' please see the Type Constants enumeration "Civil GIS Attribute Type";

a 'GIS Feature Attribute' represents a "Column" in the GIS Database table; each 'GIS Feature' (built-up from dwg entities) is a row in such table;
the 'GIS Feature Attribute' name string is always handled as case-insensitive !