NLCD Frequently Asked Questions (FAQ)

IMPORTING FLAT LAND COVER FILE INTO ARC

The following steps will help you import an 8 bit flat binary file 
(your land cover image)into Arc/Info or Arc View.  The steps required 
for each software package (Arc/Info) or (ArcView) or (Both) will be 
indicated beside the respective step number.  

(#1(Both))  Be sure you download the appropriate documentation file 
for your image (*.doc or *.readme.txt). It contains necessary 
information for correctly ingesting, displaying and registering the 
image.

{#2(Both)}  Unzip the file that you have downloaded (*.gz).  Software 
programs such as WinZip (PC) or gunzip (UNIX) can be used to 
uncompress your file.  

{#3(Both))  For Arc/Info or ArcView to recognize your image, it is 
necessary to change the file extension to '.bil'(i.e. *.bil). 

{#4(Both)}  You must also create an ASCII text header file.  Both 
Arc/Info and ArcView require a header file in order to recognize, 
ingest, and display the image.  To create the header file, it is 
critical that this file is saved as a (text only) file. Using programs
 such as MS Word or WordPerfect to create your header file will not 
create usable header files unless you specifically select text only 
'.txt'  during your save. Save your header file file in the same 
folder and with the same name as your 'bil'file but with a '.hdr' 
file extension (i.e. 'image_a.bil' and 'image_a.hdr') 

{#5(Both)}  A sample header file is shown below. See Arc documentation 
for a complete description.  The values for each keyword parameter are
 found in the documentation or 'readme' file you downloaded for your 
image file. When entering data, it is critical that tabs are not used 
to add space between each key word and its respective value. You must 
press the 'enter' key after each line of data (even the last line).  

BYTEORDER    M  	
LAYOUT       BIL 
NROWS       23328 (use value from documentation file)
NCOLS       20036 (use value from documentation file)
NBANDS      1  
NBITS       8     (16 for DEMs)
SKIPBYTES   0  	
ULXMAP      -1747230  (use value from documentation file)
ULYMAP      1701780  (use value from documentation file)
XDIM        30        (30 for NLCD, 1000 for Global products, DEMS- see .doc file)
YDIM        30        (30 for NLCD, 1000 for Global products, DEMS- see .doc file)

{#6(Both)}  Enter values show above for BYTEORDER, LAYOUT, NBANDS, 
NBITS, and SKIPBYTES, into your header file.  They are the same for 
the National Land Cover Dataset (NLCD) and Global land cover datasets 
provided by the USGS.  For DEM products, NBITS is 16.  

{#7(Both)} Enter values for NROWS, NCOLS, ULXMAP,ULYMAP, XDIM, and 
YDIM into your header file.  These values will vary for each image 
file and are located in the associated documentation file.
(a) Locate Number of Lines (rows/height): 23328 in the readme file and 
enter this value as NROWS in your header file.
(b) Locate Number of Samples (columns/width): 20036 in the readme file 
and enter this value as NCOLS in your header file. 
(c) Locate Projection Coordinates: Upper Left Corner: -1747230 
meters(X) in the readme file and enter this value as ULXMAP.
(d) Locate Projection Coordinates: Upper Left Corner: 1701780 
meters(Y) in the readme file and enter this value as ULYMAP.  

{#8(Both)} Be sure to save this file as plain text in the same folder 
as your 'bil' file and with a '.hdr' file extension.

{#9(Arc/Info)}  To view your data in Arc you will need to follow these 
steps.

(a) Access the directory and folder where the 'bil', and 'hdr' files 
are located.
(b) Start the Arc program.
(c) Start the GRID program.
(d) At the 'Grid' prompt, type Grid: display 9999
(e) At the 'Grid' prompt, type Grid: mapextent image file_name.bil
(f) At the 'Grid' prompt, type Grid: image file_name.bil

(#10(Arc/Info)) To ingest the data into GRID and define projection 
parameters:

(a) At the 'Arc' prompt, type Arc: imagegrid < filename.bil> < gridfile_name >
(b) At the 'Arc' prompt, type Arc: projectdefine grid < gridfile_name > 
and enter the projection parameters found in the documentation file.

{#11(ArcView)} Follow these steps to import and display the data 
in ArcView:

(a) Start Arc View.  
(b) Select VIEW in the Arc View task bar. Select NEW to create a 
new view window.
(c) Select the ADD theme icon
(d) Select Image Data Source In the data source types drop down menu .
(e) Locate and select the folder where you have saved your .bil and 
.hdr files.
(f) Select your 'bil' file and click OK
(g) Your image can now be viewed after selecting the image in the 
task bar of your view screen.