cessing, and one- 
ibutes to support 
ies both needs by 
npletely from the 
1g them to a new 
table whose 
bjects is indirect 
method for its 
leased "Dynamic 
neal features in 
S now correspond 
s called "routes" 
relationship with 
relationship with 
was extended to 
h the introduction 
called "regions." 
feature class for 
age. 
method are the 
control over to the system for managing the 
indirect linkage between real-world features and 
graphic objects, we introduce a level of processing 
overhead which may be undesirable when the 
occurrence of coincident features is infrequent. 
3. METHODOLOGY SELECTION 
Table 1 summarizes most of the 
considerations relevant in selecting an appropriate 
methodology for coincident feature handling. The 
left column identifies the type of system by 
feature attribute linkage type as described in 
sections 1 and 2 above. Note that advanced raster 
algorithms are ignored in this discussion to focus 
on vector systems. System requirements as shown 
in the italicized column headings are described as 
follows. 
Extended Attributes--this system allows 
multiple user attributes. 
System Topology--this system allows for 
the automatic generation of spatial descriptors and 
topological pointers. 
No Redundant Features--this system 
provides a means to avoid redundant storage of 
geographically coincident features. 
Avoids Wasted Space--data storage 
requirements are a function of data present, not 
potential features. 
Dynamic Feature Depth--this system 
allows an unlimited number of features on the 
same graphic object. 
No Extra Programming--this system is 
workable out-of-the-box without substantial 
application programming. 
Table 1. Methodology Selection Matrix 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
thod without the Extended System No Avoids Dynamic No Extra 
imming, provided Attributes Topology Redundant | Wasted Feature Program- 
bstracted feature Features Space Depth ming 
that if. we turn TTT 
Raster Coincidence ^ A / 
B Implied Attributes d v / / 
C 
A Selective User Linkage | v / V V V 
e: 
Universal System / / 
x Linkage...(1) dl 
Binary Flag Method / / V / 
5 Reserved Space / / / 
Het Method 
Zl Pee - + 
8 Auxiliary Table / / / / 
E" | Method ————— aS on oo oo m um pe mtn m vs ct ae re Doom APR PH M 
E Abstracted Feature / / / v (3) V / (4) 
© Method 
NOTES: (1)--All the following methods are workarounds for systems with universal attribute linkage. This 
rOW represents a basic universal-linkage system with no workarounds. 
(2)--The Binary Flag method requires application programming when the flags are not self- 
documenting. The powers-of-two compound flag is an example. 
(3)--The Abstracted Feature Method makes efficient use of attribute space, but does introduce a fixed 
level of overhead for system linkage to all graphic objects regardless of coincident feature 
  
requirements. Projects with very few coincident features may be more efficiently served with the 
Auxiliary Table Method. 
Feature Method (4)--Provided, of course, the system comes with this capability. ESRI's ARC/INFO, for example. 
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