Data Source: Sampled array of elevations for ground positions at regularly spaced intervals
Agency: Produced by Defense Mapping Agency, distributed by USGS
Scale: 1:250,000
Date: 1996
Data Accuracy: DEM views are checked for completeness more so than for accuracy. There may be voids due to interruptions to contours in source information. Horizontal positioning: 90% of points must be within 0.02 inches of true position. Vertical positioning: vertical root-mean-square error statistic is used, encompassing both random and systematic errors.
Method used to develop data: 1) Data acquired from NMD as 1 degree x 1 degree blocks 2) DEM files were processed to produce elevation grids 3) Elevation grids were merged to form one grid 4) Grid was projected into an albers equal-area projection 5) Mask grid was created using 1:100,000 state boundary 6) Mask grid was used to clip elevation grid to state boundary 7) A coastline coverage was used to create a mask grid of ocean and coastal waterways 8) Coastline grid was used to clip out coastline and islands
DEM's can be used as source data for digital orthophotos and as layers in GIS. They are useful tools for earth science analysis, volumetric analysis, site location of towers, and for drainage basin delineation. The DEM's may have voids, which could limit their use. Their coverage, however, is for the entire United States.
The Endangerd Tortoise and the GPS Hare: Fast Technology Comes to a Slow Critter
Project authors: Jerry E. Freilich and Robert L. Moon
Study Date: 1990
The purpose of this project was to identify, monitor, and study the population activity of the desert tortoise, listed as threatened by the U.S. Fish and Wildlife Service.
The study site is California's Joshua Tree National Monument in the Mojave Desert. The site was divided into one square kilometer study areas. The site is desolate desert, which makes it hard to find your location. "To know exactly where we were, we would have needed to survey and place 10,000 stakes at the grid corners of each 100-meter-square quadrant(GIS WORLD, 9/91, p.47)."
The team used NAV 1000 PRO Global Positioning System receivers to fix a location where a tortoise was found, and a flag was placed at the site. Universal Transverse Mercator coordinates were used to develop a desert tortoise theme in a GIS database. Coordinates are taken for located tortoises and burrows. Hypercard, MacGIS, and Claris FileMaker were used to process the data and form an image of the area, with dots representing tortoises and burrows. Each dot opens up to a window with a complete record of tortoise activity at that spot. A Canon XapShot camera was used to take still video images that were downloaded directly into the database.
The use of GIS enabled the team to study movement patterns and burrowing activities over time. It helped in determining where to concentrate their studies. GIS also allowed the team to use other data in their research, i.e. soil factors, vegetation types, and other animal species in the area. The use of GIS provided a very time and money efficient system of studying the tortoise.
I believe that this project shows how useful GIS can be. Not only did it save the team a world of money, but it minimized the time required for the study; in short, it is very efficient. This method could be used for a whole host of wildlife studies very similar to this one. The tortoise project may lead to more widespread use of GIS in the wildlife biology field, and in turn, do its part to "Save the Whales."