a GCM table used, is an excellent way to 
express them more consisely and expedient]ly. 
4. INTRODUCTION TO GCM [Ma Ainai,1988] 
At first, independent factor, an important 
concept, must be defined: it is the basic 
element of geographic phenomenon or process, 
it has quantity and cannot be ‘induced from 
another. For example, the elevation (h) is an 
independent factor, while slope is not an 
independent factor which is dh/ds in a 
contour map; The temperature (T) is an 
independent factor,while temperature gradient 
is not,because it is dT/ds in an isotherm; The 
velocity (v) is independent but discharge (Q- 
BHv) is not; The precipitation, vegetation 
coverage, soil depth are independent but soil 
erosion is not,and all that. 
Last but not least, no thematic map is a pure 
independent map, its factors are 
comprehensive,for example: 
a. Climatic map, factors generally considered 
are: 
Irradiance, Temperature, Precipitation, 
Evaporation, Elevation,etc. 
b. Hydrologic map: 
Elevation, Watershed,water discharge,sediment 
discharge,etc. 
c. Vegetation map: 
Temperature, Precipitation, Irradiance, 
Elevation, slope,aspect,Soil Granular ity,Soil 
pH Value, Vegetat ion Form, Type, Coverage ‚etc. 
d. Pedological map: 
Soil Material,soil moisture,Soil granularity, 
Soil Temperature, Soil pH Value, Soil 
Fertility, Vegetation Form, Type, Coverage ‚so i 1 
erosion intensity, Elevation,etc. 
e. Geomorphological map: 
Elevation, Form, Type, Lithologic characters, 
Structure,Temperature, Precipitation,Dynamics 
Chrono-Quaternary Period,etc. 
(Note: The factor whose first letter is 
written in caption is independent.) 
The conclusion from above are: 
a. There are many common factors between 
these thematics: such as elevation, 
temperature, and precipitation, etc. 
b. Factors that are not independent can be 
induced from independent factors. 
Giving these independent factors a series 
code according to certain law is called 
GEOCODE . 
In the GIS, if inputing these factors instead 
of thematic maps into computer can reduce 
redundancy, an expert can choose his favorite 
factors to build his own map reflecting his 
own idea, and do other relative research work 
more flexibly. 
564 
5. HOW TO MAKE GCMOODE 
5.1.2-D to 3-D 
The toporiphic map is used to be registered 
with remote sensed ‘image, so that  two- 
dimensional information is expanded to a 
three-dimensional one. 
5.2 Table of indepent factors 
As above factors, some have quantitative 
values, some have qualitative ones. And 
certain grade must be given to classify the 
independent factors. 
5.3 GCM map and and GCM table 
GCM includes a GCM table and a GCM map ( map 
of the smallest polygon ) . There has been a 
method which uses certain squared area to be 
something like the smallest polygon as has 
mentioned above. But being an artificial one, 
this kind of squared area doesn’t represent 
the polygon which really exists, and as a 
result, this method has a low precision. But 
our smallest polygon is a representation of 
certain real area which has common factors, 
thus the GCM map is more reasonable. 
Factors of GCM table: 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
E1 (m) 9. MC sd (om) 
1 «350 > 90 <20 
2 50 — 200 79 — 90 20 — 40 
3 200 -- 500 50 — 70 40 — 60 
4 500 — 1000 |30 — 50 60 — 100 
5 1000 — 1500 |10 — 30 > 100 
6 > 1500 <10 
Polygons of GCM map: 
GCM table: 
No. |(1st) El {(2nd) vc |(3rd) sd |(4th). 
A 1 4 2 
B 2 4 2 
C 3 3 1 
D 4 3 2 
E 5 2 2