There are several sources of vegetation data for the United States available on the world wide web. Many of those data sets are referred to in my research documentation. One of the best sources of vegetation data that can be utilized in a GIS is the USGS Land Cover Characteristics data. This data is part of a project to develop one kilometer vegetation data for the entire world. The data can be found at the web site http://edcwww.cr.usgs.gov/landdaac/glcc/glcc.html.

The U.S. Geological survey is developing this data in cooperation with the the University of Nebraska-Lincoln and the European Commission's DG Joint Research Centre. The data is being generated from 1-km Advanced Very High Resolution Radiometer data. The data for North America is available in two projections and six formats. The data can be obtained in either the Interrupted Goode Homolosine Projection or in the Lambert Equal Area Projection. The most detailed version of the data is referred to as the North America Seasonal Land Cover Region set and has 205 vegetation classifications. These classifications can be found at the LCC Legend.html.

Although this data base is public domain, the conversion of the data to an Arc/Info usable format is not completely obvious. The following is the process that I used to make the vegetation data useable in Arc/Info.

1. DOWNLOADING THE DATA.

Arc/Info directly supports the Lambert Azimuthal Equal Area projection so it is more convenient to use the data in this projection (especially if the coverages are to be projected into other coordinate systems). Once the desired data set is decided upon the file can be either downloaded off the web directly from the North American Land Cover Lambert Azimuthal Equal Area Projection File Listing found at http://edcwww.cr.usgs.gov/landdaac/glcc/tablambert_na.html or it can be obtained via ftp from ftp edcftp.cr.usgs.gov in the directory /pub/data/glcc/na. The files are on the order of 83 megabytes so gziped files are available.

2. PREPARING THE FILE.

The files are of .img format which is easier to use with some programs than others. There is a public domain program called ____ which can be used to view these images and can be obtained from NASA's web site (although time was not used to learn this application).

To use the data in Arc/Info the data must be converted from the .img format to a grid. First the file should be unzipped if the zipped version was downloaded. The unzipping comand in a UNIX environment is as follows.

gunzip <lcc.img>

Next the file needs to be given a "bil" extension.

mv <lcc.img> <lcc.bil>

Then a header file needs to be made for the bil file. This header file contains information on the size and location of the data set. The file can be made in any type of text editor, but it needs to be saved in the same directory as the 'bil' file and have the same name as the bil file.

lcc.hdr

The metadata needed for the header files can be found at http://edcwww.cr.usgs.gov/landdaac/glcc/nadoc.html under geometric characteristics. The header file created for the Seasonal Land Cover data set was as follows (words in parenthesis are only for explanation, do not use in actual file).

nrows	8996	(Number of rows in the data set)
ncols	9223	(Number of columns in the data set)
nbits	8	(The bit size of the image 0
ulxmap	-4486549.963	(The x-coordinate of the upper left corner of the image)
ulymap	4479868.288	(The y-coordinate of the upper left corner of the image )
xdim	1000	(Number of meters in x direction for each pixel)
ydim	1000	(Number of meters in y direction for each pixel)

 

There should now be at least two files in the working directory; <lcc.img> and <lcc.hdr>.

 

3. CONVERTING THE FILE

Now in arc convert the bil file to a grid file using the IMAGEGRID command.

Arc: imagegrid lcc.bil lcc

 

4. UPDATE THE PROJECTION INFORMATION

5. SEPARATING THE DOMAIN OF INTEREST

6. ATTACHING ATTRIBUTES TO THE FILE

The grid file that is now in the working directory does not have an attribute tale at this point. The only data that this file contains is the numerical value that represents the land cover type for each separate square kilometer. There are a couple of ways to complete the attribute table for the file depending on the software available to the GIS technician. One method is to use Info. Another is to use Arcview if that program is available.

6a. AN INFO METHOD

The following is a general outline of the procedure for attaching the attributes to the file using the Info options in Arc/Info. (It were provided by Mr. John W. Jones of the U.S. Geological Survey)

 

1.) using info, create a table that will be used to hold the attribute information: define lcc.inp

VALUE,3,5,I

CODE,3,5,I

CATEGORY,50,50,C

 

2.) use an editor to reformat the attribute file (lcc.att) for import to info. I used commas to delimit the fields, placed the character strings in quotes, and removed all blank spaces (excepting those in the strings).

 

3.) in info, "add" the data from the ascii file into the info table:

add from /home/GISuser/lcc.dat

 

4.) in arc, use "joinitem" to put the fields in lcc.inp into the vat file for the lcc2 grid:

joinitem lcc2.vat lcc.inp lcc2.vat value count

 

The grid should now be ready for use. If a polygon coverage is desired the grid can be converted using Arc:

Arc: gridpoly lcc2 lcccoverage

 

6b. AN ARCVIEW METHOD 

For the arcview method the grid is just converted to a coverage and then the additional information can then be manually added into the coverage's attribute table.

Arc: gridpoly lcc2 lcccoverage

Arc: clean lcccoverage

 

lcccoverage can now be brought into arcview and the attribute table can be modified using the table editing features. Start a new file in arcview. Open a view in arcview and bring lcccoverage into it from where it is being stored. Then click on the attribute table button in the Arcview GUI (graphical user interface). Go to 'edit table' in the edit menu. Then go to 'add field'. Name the field, indicate characters because words will be used in this attribute, and make the size of the columns large enough for the descriptions to be used. The descriptions can be determined by looking at the legend for the file being used. Now select 'add rows' for data entry into the table. Click on the hand symbol over the table and then on the places to enter data. Once the table is completed make sure that none of the cells are raised and select 'stop editing' under edit.

 

Another option in Arcview is to just use the attribute table with only the value field in it, but to design and store a legend with the corresponding descriptions in it.

 

PROJECTING THE COVERAGE INTO ANOTHER COORDINATE SYSTEM