10 METER SHALSTAB Landslide Hazard and Slope Map Images
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IMAGE NAME: garciaqt.tif

FEATURE TYPE: IMAGE in Tiff format; compression Packbit; 4 bit color format
   
SOURCE: CDF FRAP NCWAP DEM Data Distribution Release 01 and Shalstab model

MINIMUM MAPPING UNIT: 10 meters (spatial resolution)

AREAL EXTENT: Garcia project area

DATE OF LAST UPDATE:  10/10/2001

COORDINATE SYSTEM DESCRIPTION

PROJECTION:	UTM
Zone:		10
Units:		Meter	
Spheroid:	CLARKE1866
Datum:		NAD27
X Shift:	0.00000		
Y Shift:	-4000000.00


METHODS:

The shalstab landslide theme was produced as follows.

1. With Arcview Spatial Analyst clip 2 grids from the FRAP 10 meter DEM provided by CDF. Each area was approximately the size of 2 - 3 USGS 1:24,000 topo quads. Shalstab currently crashes Arcview on larger areas.

2. Buffer each of the 2 grids with a 500 meter buffer. Shalstab produces inaccurate results near the edge of an elevation grid.

3. Produce 2 slope and 2 landslide hazard grids.

4. Clip the grids back to a 200 meter buffered size so that they will slightly overlap in a merge but have problems removed.

5. Merge the 2 landslide hazard and slope grids back into one grid.

6. Produce tiffs with Arcview using the Gridimage extension from Computerra (available from the users scripts on www.esri.com); correct the worldfile + 5 meter for longitude, - 5 meter for lattitude.

7. Compress the tiffs; the final format is 4 bit color and packbit compression.


Notes on Usage

The landslide hazard map is best used in combination with DRG topo maps. Overlaying topos on top of the landslide layer produces a hybrid topo/landslide hazard map that is easy to use in the field.

The CD provides an important validation paper (dietrich98.pdf) that reviews results obtained in Northern California. This paper also provides the rational to label hazard values less than -2.8 as "high hazard".