GIRAS, LULC Vector Format

LULC (Land Use Land Cover) data for locations in the United States has been provided by the USGS (U.S. Geological Survey) over the years using several different formats.   Legacy LULC data sets are often found that use two different formats for LULC data for the same region: the GIRAS (Geographical Information Retrieval and Analysis System) vector format, and  CTG (Composite Theme Grid) raster format.   CTG format is also known as Grid Cell format since it is often published in a file called grid_cell.   LULC data in these formats can usually be found for each of the 1:100K and 1:250K regions traditionally served by USGS.  

LULC GIRAS Vector Format Files

Files in either CTG or GIRAS format do not use three-letter extensions.  For example, downloading and then decompressing any compressed files for the San Francisco 100K LULC data set from USGS will result in five files, as seen in Windows File Explorer:



One of the files, the grid_cell file, is raster data in CTG format.   The other four files contain vector data in GIRAS format.   The five files provide the following information:  



It is not always easy to remember that the grid_cell file uses a different format, so Manifold users will rename the grid_cell file to grid_cell.ctg to indicate it is a raster file in CTG format, a different format used than the other four files.  


The grid_cell.ctg file can be imported into Manifold using the CTG dataport.  The other four files can be imported into Manifold using the GIRAS vector format dataport.     For example, to import the land_use drawing we can either just double-click it and Manifold will discover it is a GIRAS format file and import it, or we could manually specify use of the .Files (GIRAS) (*.*) dataport.



To import from LULC GIRAS format:


  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the location of the file.

  3. Double-click the file desired

  4. A table and a drawing will be created.


In the example above we have double-clicked on the land_use file to import that file and to create a land_use table and a land_use Drawing drawing in the project pane.


For a step-by-step example of importing and then Styling a CTG file, see the  Example: Import CTG Grid Cell File and Style topic.



Classification Codes - The value for each pixel in the grid_cell LULC is a classification code that can be matched to a palette color to provide a more understandable display, as illustrated above.  USGS defines the following codes:


1 Urban or Built-Up Land

11 Residential

12 Commercial Services

13 Industrial

14 Transportation, Communications

15 Industrial and Commercial

16 Mixed Urban or Built-Up Land

17 Other Urban or Built-Up Land


2 Agricultural Land

21 Cropland and Pasture

22 Orchards, Groves, Vineyards, Nurseries

23 Confined Feeding Operations

24 Other Agricultural Land


3 Rangeland

31 Herbaceous Rangeland

32 Shrub and Brush Rangeland

33 Mixed Rangeland


4 Forest Land

41 Deciduous Forest Land

42 Evergreen Forest Land

43 Mixed Forest Land


5 Water

51 Streams and Canals

52 Lakes

53 Reservoirs

54 Bays and Estuaries


6 Wetland

61 Forested Wetlands

62 Non-forested Wetlands


7 Barren Land

71 Dry Salt Flats

72 Beaches

73 Sandy Areas Other than Beaches

74 Bare Exposed Rock

75 Strip Mines, Quarries, and Gravel Pits

76 Transitional Areas

77 Mixed Barren Land


8 Tundra

81 Shrub and Brush Tundra

82 Herbaceous Tundra

83 Bare Ground

84 Wet Tundra

85 Mixed Tundra


9 Perennial Snow and Ice

91 Perennial Snowfields

92 Glaciers


Oceans may be coded with a value of 2000000102 or 0.



See Also



CTG, LULC Grid Cell


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Example: An Imageserver Tutorial