Table of Contents - The Atmospheric Studies Group at TRC

Section 2: Geophysical Data Processors
2.2 Land Use Data Preprocessors (CTGCOMP and CTGPROC)
This section explains how to obtain and process Land Use data. CTGPROC, the Land Use pre-processor
currently supports 5 different formats of Land Use data. The USGS Land Use and Land Cover data in
Composite Theme Grid (CTG) format, the USGS Global Data Format, two generic formats and, the US
National Land Cover Dataset 1992 (NLCD92).
Composite Theme Grid (CTG) Land Use and Land Cover (LULC) data. CTG files are sequential ASCII
files which consist of five header records and then one grid cell per logical record. The land use code is
defined at the center point of each cell which are usually spaced 200 meters apart in both east-west and
north-south directions. The points are oriented to the UTM projection. Because these files were
historically seen to be quite large (~ 38 MB for one quadrant), the first step in processing these land use
data was to compress the data file (CTGCOMP) and then to work (CTGPROC) with the much smaller
compressed file (~ 0.5 MB). However, this step is often ignored now since computers are easily able to
handle many large file sizes at a time.
USGS Global Data Format. USGS Global Land Use. The US Geological Survey (USGS), the University
of Nebraska-Lincoln, and the European Commission’s Joint Research Centre have generated a 1-km
resolution Global Land Cover Characteristics database. Data base is available in Lambert Azimuthal
Equal Area, has a 1-km nominal spatial resolution, and are based on 1-km Advanced Very High
Resolution Radiometer (AVHRR) data spanning April 1992 through March 1993.
Generic formats. CTGPROC is able to process two different formats of Generic Data. The first Generic
data format, reads the data in the form of, Land Use category, latitude and longitude in a comma
delimited format. Numeric values of Land Use are not random and specific values need to be provided
whereafter an internal translation table converts the input data codes to the USGS codes used by the
model. The second type of generic data format allows random Land Use input data and allows the user to
map each Land Use category to specific surface parameters, that do not have to use the USGS defaults in
the model.
National Land Cover Dataset 1992 (NLCD 1992). This dataset was derived from the early to mid-1990s
Landsat Thematic Mapper satellite data, the NLCD is a 21-class land cover classification scheme applied
consistently over the United States. The spatial resolution is 30 meters and mapped in the Albers Conic
Equal Area projection, NAD-83.
2.2.1 Obtaining the Data
2.2.1.1 USGS Global Land Use Data
Follow the links on www.src.com for the Global Land Cover Database Land Use and Land Cover Data
are available from the USGS at the 1:250,000-scale with file names corresponding to the 1:250,000-scale
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