Friday, September 3, 2010

3-D Analysis


Using ESRI's 3-D analyst, I collected LIDAR points (one foot elevation points obtained by flying a plane equipped with a laser). This data was tranformed into countours, then a digital elevation model was created with the pixels colored to
represent different elevations. This model was then drapped by a 2009 aerial photography. As you can see, the program stretches the aerial photo to fit the shape of the digital elevation model. Making the aerial partially transparent, allows the elevation colors of the model come through.
This analysis shows that the area to the east of the St. Mary's River, assumed to be higher than the river, is actually lower than the bottom of the St. Mary's River.
The consequences of which are obvious.

Wednesday, August 18, 2010

Complex Geoprocessing Job



My most recent work for Nassau County involved a complex geoprocessing project using ArcGIS (version 10). The State Department of Community Affairs (DCA) required that we calculate all of the acreage of our current 2010 Future Land Use Map (FLUM) and compare with the acreage contained in our proposed 2010 FLUM. One challenging
aspect of the process was determining which parcels were "developable" and which
parcels were not developable. Simply querying the property appraisers database for "vacant" property would have yielded inaccurate results since many properties are considered to be developable even though they are not vacant (such as agricultural land, pasture land, etc.).
Another challenge was calculating the development potential of the individual parcels. Even though it sounds easy, the individual properties have different development potentials depending on what they deed acreage size is. This, of course, is different than the calculated size once the FLU categories have split the parcels into multiple pieces. To overcome this, a join between tables had to be created between the property appraisers original table and the new, recalculated table. To make things even more interesting, the Property Appraiser data has the same polygon for multiple condos. On amelia island, this resulted in a 400 acre descrepancy for the "high density" FLUM. Therefore, these records had to be collapsed into one, re-assigned use values, and then merged with the main project file. There were many other processes and steps that had to be taken, but these
were some of the biggest issues. Output from the model were several pages of acreage outputs, for urban and rural densities (developable vs. developed)