Data Manipulation and Extraction
Key Processes
Key Processes Re-Projecting Data Selecting by Attributes Exporting Data Hillshade Reclassification Conversion of Raster to Vector
Re-Projecting Data Purpose To convert a particular piece of data from one coordinate system to another Very basic and essential step in any analysis using GIS If this step is not taken any analysis preformed will be inaccurate
Projecting Data Example
Selecting By Attributes Purpose To extract desired data for analysis
Selecting By Attributes How the process works All that is really being done is manipulating data sets in 3 dimensions In 2 dimensions all that exist is (x, y) describing a particular piece of data In ArcGIS one has to think in three dimensions because even though it s a 2 dimensional map the user also had elevation data (the Z-value) So the result is (x,y,z)
Selecting By Attributes Example Future Module Work... You are trying to find the total affected population The parameters Populations residing at less than zero feet (Reclassification) Total Population (selection from a Shape File)
Selecting By Attributes (Reclassification) New Orleans Affected Area Y Y Z X
Selecting By Attributes When selecting by attributes in an Attribute table the data typically only has (x, y) values associated with them unless elevation data is used as a parameter
Example Selecting By Attributes Total population affected by the Hurricane with flood waters at zero meters (Shape File) + 783,845 People Affected 298,353 People Unaffected 1,082,198 Total Population
Exporting Data Purpose To make a temporary layer permanent in a current map If this process is not done then the file may be lost when ArcMap is closed and re-opened
Hillshade Purpose Even a DEM that has been converted to a raster is still hard to interpret. By performing a hillshade on a converted DEM, the elevation changes are more visually apparent. In short, this process is mostly for aesthetics of the data.
Hillshade Notice in the hillshade that the topographic relief is easily evident
Reclassification Purpose Reclassification of a raster, in general, is used to extract specific data (i. e. specific elevation data)
Reclassification Example Everything below 0 Meters is under water
Conversion of Raster to Vector Purpose Converting a Raster to a Vector (Shape File) enables the user to intersect other data with the raster data (i. e. Census Data)
Conversion of Raster to Vector Example Intersection of the affected area (New Orleans) and the pertinent Census Data
Delineating the Project Area
The Problem Determine the affected area that has occurred as a result of Hurricane Katrina
How to Solve the problem 1. 1 Frame the problem 2. Identify data needs 3. Identify decision i support tools 4. Locate and assemble data 5. Process and analyze data 6. 6 Generate information and report
Frame The Problem What determines the location of the problem? Water level associated with the hurricane s land fall What information is needed? The current water level in the area of New Orleans, LA
Identify Data Needs Elevation data is needed to delineate the affected area More specifically DEM Data
Identify Decision Support Tools Possible support tools for this particular situation include: Up to date field data ( (i. e. water level) An outline providing the methodology of how the data will be processed
Identify Decision Support Tools Outline of the mechanical process Each Parameter will be set by the user based on the information at hand
Locate and Assemble Data DEM data can be found at: http://atlas.lsu.edu/search/
Process and Analyze Data Part I: Acquisition, importing and processing DEMs Part t II: Creating Hill shades Part III: Reclassification of the Data
Generate Information and Report