- 976 - 
Conclusions 
Selected field work was carried out, and the results were used, 
not only to field check the air photo interpretation results, 
but also to make some comparisons between field surveys and air 
photo surveys when carrying out a detailed inventory of urban 
open space. This comparison clearly indicated the relative 
advantages of using aerial photographs as the data source in 
terms of the speed, accuracy, type and depth of detail, and 
economy which could be obtained. 
In general the overall time taken to both identify and map 
(in digital form) the type, extent and distribution of open 
space was in the order of one fifth to one tenth the time it 
took to record similar data by field survey methods. 
The problems of accessibility and visibility severely restricted 
the comprehensiveness of data acquisition during field work: 
this was particularly the case when mapping private open space. 
In marked contrast the air photo view allowed 'access' to all 
existing open space, consequently there were virtually no 'errors 
of ommission!. Whilst it is difficult to precisely quantify 
the accuracy advantage of the air photo it is quite justified 
to state that the air photo survey will virtually always be 
more (sometimes very much more) accurate than the field survey. 
With respect to the type of open space data, and the level of 
detail which can be obtained from the two sources, much depends 
on whether the comparison is made at group or sub group level. 
At group level (see Figures 2 and 5) both the air photo and field 
work can, within the constraints mentioned above, readily be 
identified. At sub group level (see Figures 6 and 11) where 
vegetation type and condition are required, the black and white 
photography is inferior to both the colour infra red and field 
work. There is however little to choose between the two latter 
sources - when using the urban open space notation shown in 
Figure 2. 
The combined effects outlined do clearly indicate that there are 
considerable economic advantages in using aerial photographs 
in general, when carrying out inventories and mapping open space, 
and colour infra red photographs in particular where details of 
surface cover and vegetation condition are required. 
Even if the photography has to be flown specially it is still 
more economical than carrying out field surveys. There is also 
the additional advantage that the photography can form an 
essential part of a permanent land data bank, and can be used as 
the prime data source for other environmental and land use 
surveys. 
Having established the substantial advantages of using aerial 
photography as the data source for identifying and mapping urban 
open space, the relative merits of black and white as against 
colour infra red photography can be pursued. 
The costs of obtaining colour infra red photography is approximately 
double that of black and white, and it requires very much better 
      
  
  
   
   
  
     
    
  
    
   
  
  
     
    
     
   
    
     
   
    
    
   
  
  
    
  
    
   
    
aa rind 
mn A v" — PS