Add a field SubW_Precip_in to this table And use the field calculator to evaluate this as [Sum_APProd] / [Sum_Shape_Area] The result is the precipitation in inches for each subwatershed. To turn in: A table giving the HydroID, Name, and mean precipitation by the Thiessen method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation? 7. Estimate basin average mean annual precipitation using Spatial Interpolation/Surface fitting. Thiessen polygons were effectively a way of defining a field based on discrete data, by associating with each point the precipitation at the nearest gage. This is probably the simplest and least sophisticated form of spatial interpolation. ArcGIS provides other spatial interpolation capabilities in the Interpolation toolbox in Spatial Analyst Tools. We will not, in this exercise, concern ourselves too much with the theory behind each of these methods. You should however be aware that there is a lot of statistical theory on the subject of interpolation, which is an active area of research. This theory should be considered before practical use of these methods. Select Spatial Analyst Tools Interpolation Spline. Use the input points from "PrecipStn" and Z value field as " AnnPrecip_in", and set the spline type as Tension with parameters as follows: The result is illustrated: Select Spatial Analyst Tools Zonal Zonal Statistics as Table. Set the inputs as follows: Click OK. A table with zonal statistics is created. This contains statistics of the value raster, in this case mean annual precipitation from Spline over the zones defined by the polygon feature class Subwatershed. The HydroID in this table may be used to join it to the attribute table for the Subwatershed feature class. As for the elevations above this joined table can be exported and examined and presented in Excel. To turn in: A table giving the HydroID, Name, and mean precipitation by the Tension Spline method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation using a Tension Spline interpolation?
Add a field SubW_Precip_in to this table And use the field calculator to evaluate this as [Sum_APProd] / [Sum_Shape_Area] The result is the precipitation in inches for each subwatershed. To turn in: A table giving the HydroID, Name, and mean precipitation by the Thiessen method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation? 7. Estimate basin average mean annual precipitation using Spatial Interpolation/Surface fitting. Thiessen polygons were effectively a way of defining a field based on discrete data, by associating with each point the precipitation at the nearest gage. This is probably the simplest and least sophisticated form of spatial interpolation. ArcGIS provides other spatial interpolation capabilities in the Interpolation toolbox in Spatial Analyst Tools. We will not, in this exercise, concern ourselves too much with the theory behind each of these methods. You should however be aware that there is a lot of statistical theory on the subject of interpolation, which is an active area of research. This theory should be considered before practical use of these methods. Select Spatial Analyst Tools Interpolation Spline. Use the input points from "PrecipStn" and Z value field as " AnnPrecip_in", and set the spline type as Tension with parameters as follows: The result is illustrated: Select Spatial Analyst Tools Zonal Zonal Statistics as Table. Set the inputs as follows: Click OK. A table with zonal statistics is created. This contains statistics of the value raster, in this case mean annual precipitation from Spline over the zones defined by the polygon feature class Subwatershed. The HydroID in this table may be used to join it to the attribute table for the Subwatershed feature class. As for the elevations above this joined table can be exported and examined and presented in Excel. To turn in: A table giving the HydroID, Name, and mean precipitation by the Tension Spline method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation using a Tension Spline interpolation?