e the 
lew or 
, must 
! what 
is the 
es for 
of 
lule in 
em as 
at the 
nly for 
ysis of 
ement 
alysis 
a or 
using 
w, the 
ut of a 
output 
TIMAP 
esota. 
| State 
tion at 
and 
loped. 
M 
corner 
hip 85 
ncipal 
; Land 
is one 
has a 
91° 3’ 
t of 24 
hasa 
)3? 13° 
= 486 
of the 
vnship 
| = 504 
of the 
6 = 12 
ounty. 
and 2 
N and 
hich is 
ie mile 
15, 22 
Land 
juarter 
Yysical 
signed 
ar and 
a GIS 
Lat = 42 12 33.77 
  
Lon = 93 27 50.30 gGpem mm 
  
  
  
  
ri 
u 
LIBIBIRIRI 
  
  
  
  
  
  
SIN 
  
84N 
  
83N 
  
  
  
  
24W|23W|22W 
Lat = 41 3S1 44.24 
  
82N 
Q1W 
  
Lon = 93 41 33,37 
  
Lot = 42 12 32.23 
Lon = 93 13 33.67 
Lat = 41 31 47.93 
Lon = 93 13 55.20 
N 98» = saw 9 X 18 
© 
© 
21 X 6 mies west = 186 V 3th PM 
Lat = 34 38 45 
Lon = 91 03 07 W 
Figure 5. U.S. Public Land Survey System 
Geographic coordinates, 0, A, h on WGS 84 of 
these monuments can be determined to first 
order accuracy. For mapping purposes these 
spherical or 3 dimensional coordinates are 
converted to plane or 2 dimensional coordinates. 
In the U.S.A. different states have different plane 
coordinates known as the State Plane 
Coordinates. In this system the distances are 
reduced to the reference surfaces and directions 
are parallel with central meridian. These 
projected distances are known as grid distances 
and directions are known as grid azimuths. In 
lowa, the Lambert conformal projection is used 
for deriving the State Plane Coordinates (X, Y) as 
X = X, * R sin 
YzR,-Rcos0 
where 6 = convergance angle = f(1) 
= geodetic azimuth - grid azimuth 
R = function of latitude 
X,, R, are the constant of the projection. 
These coordinates are convenient for mapping 
but are not suitable for engineering and 
surveying application due to distortion in scale. 
In engineering and surveying one needs surface 
distance, SD, as opposed to grid distance, GD. 
The grid distance is related to surface distance 
by 
  
> (2){2) 0+ 
K Iz 
631 
scale factor 
height of point above reference 
surface 
r = radius of the reference surface 
where K 
H 
125 +EH\ 1 
£=| ze 
Thus a local surface state plan (X, Y.) 
coordinates is developed such that 
where 
(X, Y,) - state plane 
coordinate for a central 
point in the city 
A base map created in surface state plane 
system can be transformed to state plane which 
in turn can be transformed to Geographic 
Coordinate System. 
DEVELOPMENT OF THE BASE MAP 
A major secondary goal of a GIS project is to 
develop a coordinate base map for the GIS in the 
surface state plane coordinate system. The 
direct entry of coordinate values for key points 
into a digital drawing file eliminates errors which