USGS - science for a changing world

USGS Digital Raster Graphics


DRG Home  DRG Technical Information  Standardized Data Set Names

USGS Digital Raster Graphic (DRG) Program

Note: The information on this page is being retained for technical and historical reference only. The site is not under active maintenance and may include expired information and outdated links.

Please visit The National Map and US Topo. Bookmark those links for current geospatial data from the U.S. Geological Survey.



STANDARDIZED DATA SET NAMES FOR DRG PRODUCTS

------------------------------------------------------------------------------------------------------- - 7.5-x7.5-minute
- 7.5-x15-minute
- 1:63,360 Alaska
- 30-x60-minute 1:100,000
- 1-x2-degree 1:250,000
- Pacific Islands 1:24,000

-------------------------------------------------------------------------------------------------------

 
OVERVIEW
To facilitate file manipulation by the widest possible range of potential 
users, data and text files on the CD-ROM conform to the DOS "eight plus
three" (8.3) file naming convention.  

The associated DRG image (.TIF), world (.TFW), and metadata (.FGD) files 
incorporate an intelligent data set name (DSN) consisting of descriptive 
metadata wrapped around a standardized kernel that describes
the spatial location of the file.  The intent of this file naming protocol
is to positively identify the spatial identity of the file and describe its
categoric identity.  

The DSN is designed to geographically locate DRGs of quadrangles using the
7.5-minute grid, clearly identifying those that fall exactly on the 
grid.  DRGs that are not aligned with the 7.5-minute grid can be named
with this convention but additional consideration is required to relate
these undersize, oversize, or offset quadrangles to their most logical and
unique 7.5-minute grid location.  

-------------------------------------------------------------------------------------------------------

EXAMPLE OF DSN CONVENTION APPLIED TO DRG PRODUCTS   

             LAT/LONG OF  
CATEGORY    SECONDARY CELL     MAP INDEX NUMBER        DOT    FILE TYPE     
---------   --------------     -----------------      -----   ---------
One Alpha    Five Numeric    One Alpha-One Numeric     (.)   Three Alpha
  (A)          (YYXXX)            (A)      (N)                  (TIF)    
                                   
                                      
                                AYYXXXAN.TIF 
                                      
                                   Where:
                            
                    A = Category (Series, Scale, and Class)
                   YY = Degrees Latitude (Secondary Cell)
                  XXX = Degrees Longitude (Secondary Cell)
                   AN = Map Index Number (Primary Cell)
                  TIF = Tagged Image File Format            
        

EXAMPLE:  O37091H7.TIF = Rolla, Missouri, 7.5-minute, 1:24,000-scale
Topographic Quadrangle

          Where:

             O = 7.5-minute, 1:24,000-scale Topographic Quadrangle
            37 = Degrees Latitude
           091 = Degrees Longitude
            H7 = Map Index Number for the Rolla Quadrangle
           TIF = Tagged Image File Format   

-------------------------------------------------------------------------------------------------------

DEFINITIONS:
        
CATEGORY - One alpha character identifying the series, scale, and class of
the DRG.
        
  --------------------------------------------------------
   CATEGORY          SERIES          SCALE         CLASS
  ---------------------------------------------------------
      R                     7.5'    1:20,000    Topographic
      O                     7.5'    1:24,000    Topographic
      P                     7.5'    1:24,000     Orthophoto 
      L                     7.5'    1:25,000    Topographic
      J                     7.5'    1:30,000    Topographic
      K                 7.5'x15'    1:25,000    Topographic
      I                  Alaska     1:63,360    Topographic
      G                  30'x60'   1:100,000    Planimetric
      F                  30'x60'   1:100,000    Topographic
      C            1 x 2 Degree    1:250,000    Topographic 


LAT/LONG OF SECONDARY CELL - Expressed in degrees of latitude
(2 characters) and degrees of longitude (3 characters), defining the
southeast corner (integer grid corner), of the secondary cell.   

To maintain unique DSN's throughout this series, the longitude of secondary
cells falling in the eastern hemisphere, west of 180 degrees, are
incremented upward from 180.  As an example, the southeast corner of a
1-degree secondary cell located at 52-degrees north latitude and
175-degrees east longitude (5 degrees west of 180) converts to the
following 5-character code describing the cell's location:  52185.
        
SECONDARY CELL -  1- by 1-degree cell (except Alaska) defined by
integer latitude and longitude.  Cells in Alaska vary in size, but are
always identified by integer latitude and longitude.
        
MAP INDEX NUMBER - Two-character alphanumeric code locating the primary
cell (quadrangle) within the secondary cell.

TIF - Tagged Image File Format (TIFF) - A tag based file format that is
designed to promote the interchange of digital image data.     

-------------------------------------------------------------------------------------------------------
EXAMPLES OF DATA SET NAMES BY SERIES
The following examples of Data Set Names for the DRG product  are not all 
inclusive.  Normal packaging of one 1:250,000-scale, two 1:100,000-scale, 
and sixty-four 1:24,000-scale quadrangles can involve combining several 
categories of maps on each disc.  For example, to complete a 1- by 1-degree
coverage area, it is entirely possible that a single distributable DRG CD-ROM
can contain one or more of the following map categories:

   1:24,000- and 1:25,000-scale, 7.5-minute quadrangles.     
   1:24,000-scale 7.5-minute Provisional Maps.    
   1:24,000-scale 7.5-minute Orthophotomaps.
   1:25,000-scale 7.5- by 15-minute quadrangles.

As a result, optimal packaging of sixty-four 7.5-minute quadrangles is
compromised if one or more 7.5- by 15-minute quads are included in a 1-by
1-degree cell.

-------------------------------------------------------------------------------------------------------
    
                          DATA SET NAMES
                                For
                      7.5- by 7.5-Minute Series
                   1:24,000- And 1:25,000-Scale Data
        
                               41089
        090                                             089
      42 +-----+-----+-----+-----+-----+-----+-----+-----+ 42 
         |     |     |     |     |     |     |     |     |  
         |     |     |     |     |     |     |     |     | H
         |     |     |     |     |     |     |     |     |
         +-----+-----+-----+-----+-----+-----+-----+-----+
         |     |     |     |     |     |     |     |     |
    +--->|     |     |     |     |     |     |     |     | G
    |    |     |     |     |     |     |     |     |     |   
    |    +-----+-----+-----+-----+-----+-----+-----+-----+
    |    |     |     |     |     |     |     |     |     |  
    |    |     |     |     |     |     |     |     |     | F
    |    |     |     |     |     |     |     |     |     |
    |    +-----+-----+-----+-----+-----+-----+-----+-----+
    |    |     |     |     |     |     |     |     |     |
    |    |     |     |     |     |     |     |     |     | E
    |    |     |     |     |     |     |     |     |     |   
    |    +-----+-----+-----+-----+-----+-----+-----+-----+
    |    |     |     |     |     |     |     |     |     |
    |    |     |     |     |     |     |     |     |     | D
    |    |     |     |     |     |     |     |     |     |<---+
    |    +-----+-----+-----+-----+-----+-----+-----+-----+    |
    |    |     |     |     |     |     |     |     |     |    |
    |    |     |     |     |     |     |     |     |     | c  |
    |    |     |     |     |     |     |     |     |     |    | 
    |    +-----+-----+-----+-----+-----+-----+-----+-----+    | 
    |    |     |     |     |     |     |     |     |     |    |
    |    |     |     |     |     |     |     |     |     | b  |
    |    |     |     |     |     |     |     |     |     |    |  
    |    +-----+-----+-----+-----+-----+-----+-----+-----+    |   
    |    |     |     |     |     |     |     |     |     |    |
    |    |     |     |     |     |     |     |     |     | a  |
    |    |     |     |     |     |     |     |     |     |    |  
    | 41 +-----+-----+-----+-----+-----+-----+-----+-----+ 41 |   
    |   090 8     7     6     5     4 ^   3     2     1 089   |   
    |                                 |                       |  
    |           41089a4 - identifies--+                       |
    |           41089d1 - identifies--------------------------+
    |           41089g8 - identifies--+
    |                                 |                                  
    +---------------------------------+              
                          
-----------------------------------------------
      quadrangle           full data set name
----------------------------------------------- 
 41089a4 = lacon, il.          o41089a4.tif
 41089d1 = troy grove, il.     o41089d1.tif
 41089g8 = morrison, il.    +--o41089g8.tif
                            |
                          where:
                                               
     o = 7.5-minute, 1:24,000-scale topographic quadrangle 
    41 = degrees latitude
   089 = degrees longitude         
    g8 = map index number for the morrison quadrangle
   tif = tagged image file format

-------------------------------------------------------------------------------------------------------

In the following example, the DSN identifies 7.5- by 15-minute primary
cells (quadrangles). Dotted vertical lines indicate the normal 7.5- by 7.5-
minute grid spacing.  As in the previous example, rows A through H and
columns 1 through 8 are used to determine the Map Index Number. In this
case, however, identification of the 7.5- by 15-minute primary cell is
based solely on columns 1, 3, 5, and 7.  

-------------------------------------------------------------------------------------------------------

                          DATA SET NAMES
                                For
                       7.5- by 15-Minute Series
                         1:25,000-Scale Data
        
                               42071
        072                                             071
      43 +-----------+-----------+-----------+-----------+ 43 
         |     :     |     :     |     :     |     :     |  
       H |     :     |     :     |     :     |     :     |  
         |     :     |     :     |     :     |     :     |
         +-----------+-----------+-----------+-----------+
         |     :     |     :     |     :     |     :     |
       G |     :     |     :     |     :     |     :     |  
         |     :     |     :     |     :     |     :     |   
         +-----------+-----------+-----------+-----------+
         |     :     |     :     |     :     |     :     |
       F | Ashburnham|     :     |     :     |     :     |  
    +--->|     :     |     :     |     :     |     :     | 
    |    +-----------+-----------+-----------+-----------+
    |    |     :     |     :     |     :     |     :     |  
    |  E |     :     |     :     |     :     |     :     |  
    |    |     :     |     :     |     :     |     :     |
    |    +-----------+-----------+-----------+-----------+
    |    |     :     |     :     |     :     |     :     |
    |  D |     :     |     :     |     :     |  Boston   |<---+
    |    |     :     |     :     |     :     |   north   |    |
    |    +-----------+-----------+-----------+-----------+    |
    |    |     :     |     :     |     :     |     :     |    |
    |  c |     :     |     :     |     :     |     :     |    |
    |    |     :     |     :     |     :     |     :     |    | 
    |    +-----------+-----------+-----------+-----------+    | 
    |    |     :     |     :     |     :     |     :     |    |
    |  b |     :     |     :     |     :     |     :     |    |
    |    |     :     |     :     |     :     |     :     |    |  
    |    +-----------+-----------+-----------+-----------+    |   
    |    |     :     |     :     |     :     |     :     |    |
    |  a |     :     |     :     |  franklin |     :     |    |
    |    |     :     |     :     |     :     |     :     |    |  
    | 42 +-----------+-----------+-----------+-----------+ 42 |   
    |   072 (8)   7    (6)    5    (4) ^  3    (2)    1 071   |   
    |                                  |                      |  
    |           42071a3 - identifies---+                      |
    |           42071d1 - identifies--------------------------+ 
    |           42071f7 - identifies---+                                  
    |                                  |                                  
    +----------------------------------+              
                          
--------------------------------------------------
       quadrangle             full data set name
-------------------------------------------------- 
 42071a3 = franklin, ma           k42071a3.tif
 42071d1 = boston north, ma       k42071d1.tif
 42071f7 = ashburnham, ma    +----k42071f7.tif
                             |
                           where:
                                               
          k = 7.5- by 15-minute, 1:25,000-scale topographic quadrangle
         42 = degrees latitude
        071 = degrees longitude         
         f7 = map index number for the ashburnham quadrangle
        tif = tagged image file format
                   
-------------------------------------------------------------------------------------------------------

In the example below, the Fairbanks 1:250,000-scale quadrangle comprises
three 1- by 1-degree secondary cells.  Dashed grids represent 15- by 30-
minute, 1:63,360-scale quadrangles.  Dotted lines represent 7.5- by 7.5-
minute subdivisions of sixty-four 7.5-minute cells comprising the 1-degree
cell.  These cells are the primary identifiers of the map locations based
on the position of the 7.5-minute cell nearest the southeast corner of each
1:63,360-scale quadrangle.  

-------------------------------------------------------------------------------------------------------

                         DATA SET NAMES 
                               For
                    Alaska 1:63,360-Scale Data

                       FAIRBANKS (1:250,000) 

        150             149             148             147   
            7   5   3   1   7   5   3   1   7   5   3   1
      65 +-------+-------+-------+-------+-------+-------+ 65 
         | : : : | : : : | : : : | : : : | : : : | : : : |          
       H | : : : | : : : | : : : | : : : | : : : | : : : | H        
    +--->|.:.D6:.|.:.D5:.|.:.D4:.|.:.D3:.|.:.D2:.|.:.D1:.|          
    |    | : : : | : : : | : : : | : : : | : : : | : : : |          
    |  G | : : : | : : : | : : : | : : : | : : : | : : : | G
    |    +-------+-------+-------+-------+-------+-------+    
    |    | : : : | : : : | : : : | : : : | : : : | : : : |          
    |  F | : : : | : : : | : : : | : : : | : : : | : : : | F        
    |    |.:.C6:.|.:.C5:.|.:.C4:.|.:.C3:.|.:.C2:.|.:.C1:.|<---+     
    |    | : : : | : : : | : : : | : : : | : : : | : : : |    |     
    |  e | : : : | : : : | : : : | : : : | : : : | : : : | e  |
    |    +-------+-------+-------+-------+-------+-------+    |
    |    | : : : | : : : | : : : | : : : | : : : | : : : |    |     
    |  d | : : : | : : : | : : : | : : : | : : : | : : : | d  |    
    |    |.:.b6:.|.:.b5:.|.:.b4:.|.:.b3:.|.:.b2:.|.:.b1:.|    |     
    |    | : : : | : : : | : : : | : : : | : : : | : : : |    |     
    |  c | : : : | : : : | : : : | : : : | : : : | : : : | c  |
    |    +-------+-------+-------+-------+-------+-------+    |
    |    | : : : | : : : | : : : | : : : | : : : | : : : |    |     
    |  b | : : : | : : : | : : : | : : : | : : : | : : : | b  |     
    |    |.:.a6:.|.:.a5:.|.:.a4:.|.:.a3:.|.:.a2:.|.:.a1:.|    |     
    |    | : : : | : : : | : : : | : : : | : : : | : : : |    |     
    |  a | : : : | : : : | : : : | : : : | : : : | : : : | a  |
    | 64 +-------+-------+-------+-------+-------+-------+ 64 |
    |       7   5   3   1   7   5   3 ^ 1   7   5   3   1     |
    |   150             149           | 148             147   |
    |                                 |                       |  
    |            64148a1 - identifies-+                       |  
    |            64147e1 - identifies-------------------------+ 
    |            64149g5 - identifies-+                                  
    |                                 |         
    +---------------------------------+                                  
                                                                        
----------------------------------------------
      quadrangle           full data set name
----------------------------------------------
 64148a1 = fairbanks (a3)     i64148a1.tif                 
 64147e1 = fairbanks (c1)     i64147e1.tif
 64149g5 = fairbanks (d6) +---i64149g5.tif
                          |
                        where: 
 
    i = alaska, 1:63,360-scale topographic quadrangle
   64 = degrees latitude
  147 = degrees longitude
   g5 = map index number for the fairbanks (d6) quadrangle
  tif = tagged image file format
                                              
                                              
-------------------------------------------------------------------------------------------------------
                    
                          DATA SET NAMES
                                For
                       30- by 60-Minute Series
                        1:100,000-Scale Data
                 
                 091                             090
               39 +-------------------------------+ 39
                  |                               |
                  |                               |
                  |                               |
                  |           38090-E1            |
            +---->|           ST LOUIS            |
            |     |                               |
            |     |                               |
            |     |                               |
            |     |                               |
            |     +-------------------------------+
            |     |                               |
            |     |                               |
            |     |                               |
            |     |           38090-A1            |
            |     |            FESTUS             |<----+
            |     |                               |     |
            |     |                               |     |
            |     |                               |     |
            |     |                               |     |
            |  38 +-------------------------------+ 38  |
            |    091                             090    |
            |                                           |
            |       38090a1 - identifies----------------+
            |       38090e1 - identifies--+
            |                             |
            +-----------------------------+

----------------------------------------------------          
       quadrangle              full data set name
----------------------------------------------------
 38090a1 = festus, mo.           f38090a1.tif
 38090e1 = st. louis, mo.    +---f38090e1.tif
                             |
                           where:
                               
        f = 1:100,000-scale, 30- by 60-minute topographic quadrangle
       38 = degrees latitude 
      090 = degrees longitude
       e1 = map index number for the st. louis quadrangle
      tif = tagged image file format
                                                
-------------------------------------------------------------------------------------------------------

In the following example, the dotted vertical line represents the division
between the east and west 1-degree secondary cells of the 1:250,000-scale
quadrangle for illustrative purposes only.
                        
-------------------------------------------------------------------------------------------------------


                           DATA SET NAMES 
                                  For
                         1- by 2-Degree Series
                         1:250,000-Scale Data
                 
                 094              093               092
               39 +----------------------------------+ 39
                  |                :                 |
                  |                :                 |
                  |                :                 |
                  |                :                 |
                  |             38092-A1             |
                  |          JEFFERSON CITY          |<----+
                  |                :                 |     |
                  |                :                 |     |
                  |                :                 |     |
                  |                :                 |     |
                  |                :                 |     |
               38 +----------------------------------+ 38  |
                 094              093               092    |
                                                           |
                    38092a1 - identifies-------------------+
                                           
--------------------------------------------------          
      quadrangle              full data set name
--------------------------------------------------
 38092a1 = jefferson city     +---c38092a1.tif
                              |
                            where:                         
     
     c = 1:250,000-scale, 1- by 2-degree topographic quadrangle
    38 = degrees latitude 
   092 = degrees longitude
    a1 = map index number for the jefferson city quadrangle
   tif = tagged image file format
                                                
-------------------------------------------------------------------------------------------------------

The following two examples describe cases where the products to be named do
not conform to the normal grid.  The examples illustrate the process of
naming quads that are undersized, oversized, or off set in relationship to
the regular 7.5-minute grid.

-------------------------------------------------------------------------------------------------------

                                
                                 Example 1
   
                              DATA SET NAMES 
                                    For 
                        The Pacific Islands (Guam)
                          Shifted Undersize Quads  
                            1:24,000-Scale Data
                        
                                   13145  
        144                                                     145
      14 +------+------+------+------+------+------+------+------+ 14 
         |      |      |      |      |      |      |      |      |  
         |      |      |      |      |      |      |      |      | H
         |      |      |      |      |      |      |      |      |
         +------+------+------+------+------+------+------+------+
         |      |      |      |      |      |      |      |      |
         |      |      |      |      |      |      |      |      | G
         |      |      |      |      |      |      |      |      |   
         +------+------+------+------+------+------+------+------+
         |      |      |      |      |      |      |      |      |
         |      |      |      |      |      |      |      |      | F
         |      |      |      |      |      |      |  .......    | 
         +------+------+------+------+------+------+--:     :....+ 
         |      |      |      |      |      |      |  :  A  :    :  
         |      |      |      |      |      |      |  :     :  B : E
         |      |      |      |      |    ............:.....:    :
         +------+------+------+------+----:     :     :     :....+
         |      |      |      |      |    :  C  :  D  :  E  :    |
         |      |      |      |      |    :     :     :     :    | D
         |      |      |      |      |    :.....:.....:.....:    |
         +------+------+------+------+----:     :     :---+------+
         |      |      |      |      |    :  F  :  G  :   |      |
         |      |      |      |      |    :     :     :   |      | C
         |      |      |      |      |    :.....:.....:   |      |   
         +------+------+------+------+----:     :     :---+------+
         |      |      |      |      |    :  H  :  J  :   |      |
         |      |      |      |      |    :     :     :   |      | B
         |      |      |      |      |    :.....:.....:   |      |
         +------+------+------+------+------+------+------+------+
         |      |      |      |      |      |      |      |      |
         |      |      |      |      |      |      |      |      | A
         |      |      |      |      |      |      |      |      |   
      13 +------+------+------+------+------+------+------+------+ 13
        144  8     7      6      5      4      3       2     1  145        
     
        
Dashed grids represent the normal 7.5- by 7.5-minute quadrangles (primary
cells) comprising the 1- by 1-degree secondary cell. 

Dotted grids represent undersize USGS quadrangles that have been shifted
from the normal 7.5- by 7.5-minute configuration to cover land. Uppercase
letters (A-J) within each dotted grid represent individual quadrangles. 


-----------------------------------------------------------
   Quad name               Secondary cell and series number  
-----------------------------------------------------------
 Inarajan (J)                         13145B2
 Merizo (H)                           13145B3
 Talofofo (G)                         13145C2    
 Agat (F)                             13145C3    
 Dededo (E)                           13145D1    
 Agana (D)                            13145D2
 Apra Harbor (C)                      13145D3
 Pati Point (B)                       13145E1
 Retidian Point (A)                   13145E2
------------------------------------------------------------------


Full data set names for the above examples:
                                                   
 Inarajan............................O13145B2.TIF
 Merizo..............................O13145B3.TIF
 Talofofo............................O13145C2.TIF
 Agat................................O13145C3.TIF
 Dededo..............................O13145D1.TIF
 Agana...............................O13145D2.TIF
 Apra Harbor.........................O13145D3.TIF
 Pati Point..........................O13145E1.TIF
 Retidian Point......................O13145E2.TIF
                                          |
                                          |
                                        Where: 
                                 
                     O = 1:24,000-scale Topographic Quadrangle
                    13 = Degrees Latitude
                   145 = Degrees Longitude
                    E2 = Map Index Number for the Retidian Point Quadrangle 
                   TIF = Tagged Image File Format

Example 1 illustrates the hierarchy for determining cells and series
numbers for quadrangles that are not aligned with the 7.5-minute grid
(undersized/offset).  Quads C, D, E, F, G, H, and J assume the series
number assigned to the primary cell in which their southeast corner lies. 
The position of the southeast corner, or nearest southeast cell corner, is
the PRINCIPAL determinant of series number within the secondary cell.

However, the southeast corners of quads A and B fall in primary cell
E1 so the NEXT determining factor is the percentage of area in the
quadrangles bounded by this cell.  In this case all of quad B is
bound by primary cell E1, while a relatively small portion of quad A is
bounded by the E1 cell.  As a result, quadrangle B is assigned to the E1
cell. 

Quadrangle A is assigned to the primary cell associated with
the cell bounding the most area within the quad that is not already
assigned to another quad.  In this case quadrangle A is assigned
to cell E2.  To properly determine the series number,  all
the surrounding quads must be considered.            

-------------------------------------------------------------------------------------------------------
                             
                            Example 2

                          DATA SET NAMES
                                For
                 The Pacific Islands (Pohnpei Islands)  
                 Overedge, Oversize and Shifted Quads
                        1:25,000-Scale Data
                   
                               
        158                                             159
         +---................----+-----+-----+-----+-----+
07201    |   :              :    |     |     |     |     |    07201
----- 07 +===:      A       :====+=====+=====+=====+=====+ 07 -----
06201    |   :              :    |     |     |     |     |    06201
         |   :..............:    |     |     |     |     | H
         |   :              :    |     |     |     |     |
         +---:      B       :----+-----+-----+-----+-----+
         |   :              :    |     |     |     |     |
         |   :..............:    |     |     |     |     | G
         |     |     |     |     |     |     |     |     |   
         +-----+-----+-----+-----+-----+-----+-----+-----+
         |     |     |     |     |     |     |     |     |
         |     |     |     |     |     |     |     |     | F
         |     |     |     |     |     |     |     |     | 
         +-----+-----+-----+-----+-----+-----+-----+-----+
         |     |     |     |     |     |     |     |     |  
         |     |     |     |     |     |     |     |     | E
         |     |     |     |     |     |     |     |     |
         +-----+-----+-----+-----+-----+-----+-----+-----+
         |     |     |     |     |     |     |     |     |
         |     |     |     |     |     |     |     |     | D
         |     |     |     |     |     |     |     |     |            
         +-----+-----+-----+-----+-----+-----+-----+-----+            
         |     |     |     |     |     |     |     |     |            
         |     |     |     |     |     |     |     |     | C          
         |     |     |     |     |     |     |     |     |             
         +-----+-----+-----+-----+-----+-----+-----+-----+             
         |     |     |     |     |     |     |     |     |            
         |     |     |     |     |     |     |     |     | B          
         |     |     |     |     |     |     |     |     |              
         +-----+-----+-----+-----+-----+-----+-----+-----+               
         |     |     |     |     |     |     |     |     |            
         |     |     |     |     |     |     |     |     | A          
         |     |     |     |     |     |     |     |     |              
      06 +-----+-----+-----+-----+-----+-----+-----+-----+ 06            
        158 8     7     6     5     4     3     2     1 159              


Dashed grids represent the normal 7.5- by 7.5-minute quadrangles (primary
cells) comprising the 1- by 1-degree secondary cell.  This particular
secondary cell is extended to the north above 7 degrees latitude to include
the Pohnpei North (H5) oversize quadrangle.

Dotted grids represent oversize USGS quadrangles that have been shifted
from the normal 7.5- by 7.5-minute configuration to cover land. Uppercase
letters A and B within each dotted grid represent individual quadrangles. 

-------------------------------------------------------------
   Quad name             Secondary cell and series number  
-------------------------------------------------------------
 Pohnpei South (B)                  L06159G5
 Pohnpei North (A)                  L06159H5         
--------------------------------------------------------------


Full data set names for the above examples:
                                                   
 Pohnpei South (B)................L06159G5.TIF
 Pohnpei North (A)................L06159H5.TIF
                                        |
                                        |
                                      Where:
                                  
                     L = 1:25,000-scale Topographic Quadrangle
                    06 = Degrees Latitude
                   159 = Degrees Longitude
                    H5 = Map Index Number for the Pohnpei North Quadrangle  
                   TIF = Tagged Image File Format

Example 2 illustrates possible overedge quad configurations that often
occur in island areas.  Graphics are shifted and adjusted in size to
minimize the number of map sheets required to effect coverage of island
land masses. 

These can be solved as illustrated for proper data set name
identification.  If the quad has an overedge that is adjacent to the
southeast corner of the cell, the normal southeast corner coordinates of
the 7.5-minute grid intersection is used for DSN determination.

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://topomaps.usgs.gov/drg/drg_name.html
Page Contact Information: Contact USGS
Page Last Modified: Monday, 14-Jan-2013 19:34:38 EST