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A processing software package, the Unified Cartographic 
Line Graph Encoding System (UCLGES) along with the digitiz 
ing syntax employed, establishes the topological relation 
ships within the data file. The resulting DLG file 
contains three types of information: a) feature codes 
(attributes) that describe the node, line or area or some 
characteristic of the elements, b) the X and Y coordinate 
values representing the relative location of the element, 
and c) topological codes which define spatial relationships 
(USGS, 1981). 
GENERAL DISCUSSION 
Interactive Techniques 
In the process of land net computation one must first con 
sider those source material elements defined as con 
straints. Categorized by reliability/accuracy and deriva 
tion of coordinate value, the following are examples: 
a) surveyed corners established by geodetic methods, 
b) paneled corners integrated through an aerotriangulation 
adjustment, c) aerial photo-identified corners plotted 
during stereocompilation, and d) corner coordinates 
furnished by other federal, state, and local government 
agencies. 
Beginning with a two-dimensional array of nodes (minimally 
49 and sometimes more than 150 per 7.5-minute quadrangle) 
which are interconnected by vectors (delineated by land 
plat data), the first task phase must accomplish a best 
mathematical fit between constraints via connecting links 
from the given vector values. This implies a certain in 
ternal cohesiveness between land plat courses (defined as 
bearings and distances) and the superimposed constraint 
coordinates. The following computational plan is dependent 
on the geometry of the township plat relative to the geome 
try of the constraints. By use of an interactive graphics 
system, the user can exercise the option of changing the 
chronological order/route dependency of traverse computa 
tions as a dependent function of closures and rejection/ 
selection of constraints. 
Prior to the advent of interactive graphics hardware, ad 
justment computations of post-1910 townships were done on a 
paper tape equipped I/O minicomputer (RPC 4000), which was 
not only cumbersome for the computational phase, but re 
quired paper tape to card deck transition (via IBM 360 
System), for Autoplot processing to produce a graphics 
product. In contrast, the interactive graphics system 
should reduce the total time requirement by 50-75 percent 
compared with former manual methods. 
1968-1975 Mapping Experience 
The Autoplot-generated public land surveys separate, a 
byproduct of the 8-year township computational program, met 
with varying degrees of success. Those townships where a