A terminal device for use with a wireless telecommunications network, the terminal device comprising: sensor circuitry configured to detect a value of a parameter which is variable in response to a variation in vertical position of the terminal device; receiver circuitry configured to receive, from infrastructure equipment of the wireless telecommunications network, a reference value of the parameter and a reference value of the vertical position at which the reference value of the parameter is associated, the reference value of the vertical position being defined relative to a first reference vertical position; processing circuitry configured to determine a value of the vertical position of the terminal device defined relative to a second reference vertical position, the second reference vertical position being ground elevation at a geographical position of the terminal device, wherein the determining comprises: determining the second reference vertical position based on a geographical position of the terminal device; determining a value of the vertical position of the terminal device defined relative to the first reference vertical position based on the detected value of the parameter, the reference value of the parameter, the reference value of the vertical position at which the reference value of the parameter is associated and a predetermined relationship between the variation in the value of the parameter and the variation in vertical position of the terminal device; determining the value of the vertical position of the terminal device defined relative to the second reference vertical position based on a difference between the determined value of the vertical position of the terminal device defined relative to the first reference vertical position and the second reference vertical position; and characterized by: receiving, from the infrastructure equipment, data indicative of the ground elevation at the geographical position of the terminal device, the data comprising geomorphological information associated with the geographical position of the terminal device. sensor circuitry configured to detect a value of a parameter which is variable in response to a variation in vertical position of the terminal device; receiver circuitry configured to receive, from infrastructure equipment of the wireless telecommunications network, a reference value of the parameter and a reference value of the vertical position at which the reference value of the parameter is associated, the reference value of the vertical position being defined relative to a first reference vertical position; processing circuitry configured to determine a value of the vertical position of the terminal device defined relative to a second reference vertical position, the second reference vertical position being ground elevation at a geographical position of the terminal device, wherein the determining comprises: determining the second reference vertical position based on a geographical position of the terminal device; determining a value of the vertical position of the terminal device defined relative to the first reference vertical position based on the detected value of the parameter, the reference value of the parameter, the reference value of the vertical position at which the reference value of the parameter is associated and a predetermined relationship between the variation in the value of the parameter and the variation in vertical position of the terminal device; determining the value of the vertical position of the terminal device defined relative to the second reference vertical position based on a difference between the determined value of the vertical position of the terminal device defined relative to the first reference vertical position and the second reference vertical position; and characterized by: receiving, from the infrastructure equipment, data indicative of the ground elevation at the geographical position of the terminal device, the data comprising geomorphological information associated with the geographical position of the terminal device. determining the second reference vertical position based on a geographical position of the terminal device; determining a value of the vertical position of the terminal device defined relative to the first reference vertical position based on the detected value of the parameter, the reference value of the parameter, the reference value of the vertical position at which the reference value of the parameter is associated and a predetermined relationship between the variation in the value of the parameter and the variation in vertical position of the terminal device; determining the value of the vertical position of the terminal device defined relative to the second reference vertical position based on a difference between the determined value of the vertical position of the terminal device defined relative to the first reference vertical position and the second reference vertical position; and characterized by: receiving, from the infrastructure equipment, data indicative of the ground elevation at the geographical position of the terminal device, the data comprising geomorphological information associated with the geographical position of the terminal device.