The Luftwaffe Map Reference System (Gradnetzmeldeverfahren)

Introduction
The official name for the map reference system of the WWII German Luftwaffe was ’Gradnetz’ or ’Gradnetzmeldeverfahren’. The system was introduced before WWII, and was in use without major modifications until end of April 1943. The escalation in the number of allied bomber attacks against targets in Germany and German occupied territory made it necessary to modify the system. The result was the introduction of the ’Jagdtrapez’ by the head of the Luftwaffe Intelligence Forces, General der Ln-Truppe Martini.

Description of the ’Gradnetzmeldeverfahren’
The idea behind the ’Gradnetzmeldeverfahren’ was to develop a system where bases and navigation points could be given a position both in maps prepared by the armed forces but also other available maps. It was based on the Greenwich system, which describe a given position by longitude and latitude, measured in degrees. This meant that the system could be used on all maps, which were made utilizing the widespread Greenwich geographic coordinate system, regardless of scale or projection used when preparing the map.
The numbers used to give the position of a certain location using the ’Gradnetzmeldeverfahren’ can be viewed as a short form of the position in full, without a real translation or encoding. The basic division have its base at the 0°-meridian (Greenwich), and have division lines at every 10° longitude. The areas between every tenth degree longitude are limited to the north and south by the 89°, 79°, 69°, 59°…and so on degree latitude. These areas, which are limited by sides measuring ten degrees longitude and latitude are called ’Zusatzzahlgebiete’.

The ’Zusatzzahlgebiete’
Every ’Zusatzzahl’ therefore describe an area contained within every tenth degree longitude and latitude. The basis for the latitudinal description of the border of the ’Zusatzzahlgebiet’ is 1° southern latitude (1° south of Equator) with a division line on every tenth degree northern and southern latitude. The corresponding basis for the longitudinal description is the Greenwich 0°-meridian, with division lines on every tenth degree eastern and western longitude.

The ’Zusatzzahl’ are given by the ten-count of the northwestern corner of each ’Zusatzzahlgebiet’. The first number give the ten-count of the longitude, while the second number give the ten-count of the latitude. If the degree number is below 10°, a zero is used. The repetition of the ’Zusatzzahl’ in the four quarters of the globe, make the use of a special description necessary; north of 1° southern latitude the ’Zusatzzahl’ for the areas having eastern longitude are given the additional description ’Ost’, while the areas having western longitude have the addition ’West’. South of 1° southern latitude the ’Zusatzzahl’ for the areas having eastern longitude are given the additional description ’Südost’, while the areas having western longitude have the addition ’Südwest’.

The ’Großtrapez’
The subdivision of the ’Zusatzzahlgebiete’ follow every whole degree longitude and latitude. The area between two neighboring degrees latitude and longitude are called a ’Großtrapez’, which can be further subdivided given the needed degree of accuracy. The 100 ’Großtrapeze’ included in one ’Zusatzzahlgebiet’ are given numbers ranging from ’00’ to ’99’. Be aware of the different numbering system for areas west and east of the Greenwich 0°-meridian.
The size of a ’Großtrapeze’ is approximately 70x111 kilometers (in Germany and other areas with the same latitudinal width).
The two-digit numbering are calculated in the following way: Using the northwestern corner of the ’Zusatzzahlgebiet’ as basis, the first number is defined by the one-count of the geographical longitude (numbers on the upper and lower edge of the map), while the second number is defined by the one-count of the geographical latitude (numbers on the left and right edge of the map).

Subdividing the ’Großtrapez’:

The ’Mitteltrapez’
The first subdivision of the ’Großtrapez’ is the ’Mitteltrapez’, which have an area of approximately 35x28 kilometers. Using the latitudinal parallels at 15’, 30’ and 45’ and the longitudinal meridian at 30’, every ’Großtrapez’ are divided into eight ’Mitteltrapeze’.
The ’Mitteltrapeze’ are numbered from ’1’ through ’8’ starting with the area in the upper left corner and ending with the lower right one.

The ’Kleintrapez’
The second subdivision define the ’Kleintrapeze’ measuring approximately 9x11 kilometers. The latitudinal parallels with 5’ distance between them and the longitudinal parallels 10’ apart, divide the ’Mitteltrapez’ into nine ’Kleintrapeze’. The numbering of the ’Kleintrapeze’ run from ’1’ through ’9’, starting in the upper left corner, making three rows of ’Kleintrapeze’, with the ninth positioned in the lower right corner of the ’Mitteltrapez’.

The ’Meldetrapez’
The third subdivision is called ’Meldetrapeze’ and have an area of approximately 3x4 kilometers. The latitudinal parallels positioned at 1’40”, 3’20”, 6’40” and 8’20” and the longitudinal parallels positioned at 3’20” and 6’40” divide the ’Kleintrapez’ into nine ’Meldetrapeze’.
The size of the resulting ’Meldetrapez’ was usually small enough as to give the necessary degree of accuracy for the report of a given position.
The numbering of the ’Meldetrapeze’ run from ’1’ through ’9’, starting in the upper left corner, making three rows of ’Meldetrapeze’, with the ninth positioned in the lower right corner of the ’Kleintrapez’.
In the system used until 30. April 1943, there were only four ’Meldetrapeze’ in a ’Kleintrapez’, numbered from ’1’ through ’4’.

The ’Arbeitstrapez’
The fourth subdivision results in the definition of an ’Arbeitstrapez’ with an area of approximately 1x1,2 kilometers by a further subdivision by a factor three the distance between the parallels in the ’Meldetrapez’. The description of the ’Arbeitstrapeze’ are given by small letters from ’a’ through ’i’, running in three rows starting in the upper left corner of the ’Meldetrapez’. In the old system, there were only four ’Arbeitstrapeze’ named ’links oben’ (lo), ’rechts oben’ (ro), ’links unten’ (lu) and finally ’rechts unten’ (ru).

’Jägermeldenetz’
For the guidance of fighter aircraft, anti-aircraft artillery and early warning systems, another system was also in use by the Luftwaffe. In the ’Jägermeldenetz’, the ’Zusatzzahlgebiete’ were divided in a northern and a southern part, these subdivisions called ’Jagdtrapeze’. As an example, the ’Zusatzzahlgebiet’ ’05 Ost’ would be subdivided into the ’Jagdtrapeze’ ’05 Ost Nord’ and ’05 Ost Süd’. The subdivision of the ’Jagdtrapeze’ was made using the same system as on the ’Großtrapeze’, dividing along whole degrees latitude and longitude. The ’Mitteltrapeze’ was given other descriptions, not two numbers but two upper letters. Starting in the northwestern corner running in rows from west to east and north to south, the descriptions started with ’AA’, ’AB’, ’AC’ and so on until ’AU’, then ’BA’, ’BB’ all the way through to ’UU’. The double letter areas cover the whole ’Jagdtrapez’, without regard to the ’Großtrapez’.

One important addition: The letter ’I’ is not used in the annotation!!!! This caused one of my research friends a considerate headache, when trying to test my example below!!!

Example of the two systems in use:
The airfield at Köln-Butzweilerhof has the following geographical coordinates:

50° 59’ 28” northern latitude and 6° 53’ 42” eastern longitude

The position in the ’Gradnetzmeldeverfahren’ is:

05 Ost 61 2 3 2 a
1 2 3 4 5 6
In the ’Jägermeldenetz’ the resulting position is defined by:
05 Ost S NO 3 2 a
1 2 3 4 5 6

The positions are found in the following way:
1. The area defined by the ten-count of the northwestern corner of the ’Zusatzzahlgebiet’. The area is limited by:
in the west 00° longitude
in the north 59° northern latitude
in the east 10° eastern longitude
in the south 49° northern latitude
In the nortwestern corner, the 00° longitude (ten-count 0) and the 59° northern latitude (ten-count 5) cross, giving the resulting ’Zusatzzahl’ ’05 Ost’. In the ’Jägermeldenetz’, the airfield is located in the southern half of the ’Zusatzzahlgebiet’, and the ’Zusatzzahl’ is ’05 Ost Süd’ or ’05 Ost S’.
2. The definition of the ’Großtrapez’ is given by the ’Gradnetzzahlen’ of the northwestern corner, in this case the cross between 06° eastern longitude and 51° northern latitude, resulting in the number ’61’ for the ’Großtrapez’.
3. The ’Mitteltrapez’ will in this case be defined by the number ’2’ in the ’Gradnetzmeldeverfahren’ system, the corresponding letter combination being ’NO’ in the ’Jägermeldenetz’.
4. ’Kleintrapez’ in both cases ’3’.
5. ’Meldetrapez’ in both cases ’2’.
6. ’Arbeitstrapez’ in both cases ’a’.
As a last comment: The Army and Navy both used other ’Gradnetzmeldeverfahren’ which did not correspond to the Luftwaffe system. Great………