QUAD Naming Convention
Quad name format was developed by the USGS and is used to
specify the geographic location of a quad map in latitude /
longitude coordinates. For example, for quad name O34119d6, the
letter "O" specifies the map scale 1:24,000. The number 34
specifies base latitude of 34 degrees, and the number 119
specifies base longitude of 119 degrees.
Each 1:24,000 map location is 7.5 minutes by 7.5 minutes; which
equates to 8 x 8 = 64 quad locations in a 1 degree by 1 degree
square of geographical area. The 8 rows and 8 columns of quad
locations within each square degree are designated by the last
2 letters of the quad name. In this example (O34119d6), the quad
is the fourth row (the letter 'd'), and sixth column (the digit
'6'). Rows are designated from 'a' (south-most) to 'h'
(north-most), and columns are designated from '1' (east-most) to
'8' (west-most). The 64 quad locations for the example are:
|
Latitude 35
|
Longitude 120
|
h8 |
h7 |
h6 |
h5 |
h4 |
h3 |
h2 |
h1 |
g8 |
g7 |
g6 |
g5 |
g4 |
g3 |
g2 |
g1 |
f8 |
f7 |
f6 |
f5 |
f4 |
f3 |
f2 |
f1 |
e8 |
e7 |
e6 |
e5 |
e4 |
e3 |
e2 |
e1 |
d8 |
d7 |
d6 |
d5 |
d4 |
d3 |
d2 |
d1 |
c8 |
c7 |
c6 |
c5 |
c4 |
c3 |
c2 |
c1 |
b8 |
b7 |
c6 |
b5 |
b4 |
b3 |
b2 |
b1 |
a8 |
a7 |
a6 |
a5 |
a4 |
a3 |
a2 |
a1 |
|
Longitude 119
|
|
Latitude 34
|
|
The following table lists the partial degree values for the bottom (south) edge of each quad location:
|
decimal |
minutes/seconds |
a |
0.000 |
00' 00" |
b |
0.125 |
07' 30" |
c |
0.250 |
15' 00" |
d |
0.375 |
22' 30" |
e |
0.500 |
30' 00" |
f |
0.625 |
37' 30" |
g |
0.750 |
45' 00" |
h |
0.875 |
52' 30" |
The following table list the partial degree values for the right (east) edge of each quad location:
|
decimal |
minutes/seconds |
1 |
0.000 |
00' 00" |
2 |
0.125 |
07' 30" |
3 |
0.250 |
15' 00" |
4 |
0.375 |
22' 30" |
5 |
0.500 |
30' 00" |
6 |
0.625 |
37' 30" |
7 |
0.750 |
45' 00" |
8 |
0.875 |
52' 30" |
For a more detailed description of quad name standards, see:
"USGS DRG Naming Convention"
|