Under Construction Continued from page 55 4. Next, join the Chuckanut Ridge Road table to the Middle Ordinates table. Right-click on the Chuckanut Ridge Road layer, choose Joins and Relates > Join and use TURN_NO as the field in this layer to base the join on, choose Middle Ordinates as the table to join to this layer, choose Turn_No as the field in the table to join on, and click on the radio button to keep all records. 5. Right-click on MO_L_FT and use the Field Calculator to populate the MO_L_FT field using values from MidOrd1.Length_Ft. 6. Now the radii of all 47 turns can be calculated. In the Chuckanut Ridge Road table, select all turns by attribute using the formula ([TURN_NO] > 0). 7. Right-click on TURNRADIUS and open the Field Calculator. Type (([CH_L_Ft]^2) / (8 * [MO_L_Ft])) + ([MO_L_Ft] /2) in the formula box. This is the algebraic form of the radius curve formula. Check to verify that all selected records calculate properly. Values will range from just under 25 feet to over 200 feet. 8. To label and study these turns, open the Properties dialog box for Chuckanut Ridge Road and select the Labels tab. Click the Expression button and type "T "& [TURN_NO] &VBNewLine & Round([TURNRADIUS],0) &"Ft" in the Expression box. Change the font to Arial 14 point and apply a halo. Click OK twice to apply the labels and make sure the Label Features box is checked. Inspect them to verify each turn number and radius. Turn the background image on and navigate back to CR MP 0.5 1:1,500. Join the Chuckanut Ridge Road attribute table with the Turn Chords table using the Turn_No field. Use an expression to label the radius of the turns. 9. To apply a thematic legend to these curves based on the turn radius, navigate to \Chuckanut \SHPFiles\WASP83NFH and load Turn Radius, Ft.lyr. Turn off the Chuckanut Ridge Road layer and check the turns. This Turn Radius, Ft.lyr uses the edited road file and applies a color legend that shows the tightest turns with thick red lines. 10. Inspect the map using the extent obtained with the MP 0.5 bookmark. Notice how all the switchback turns at approximately MP 0.7 have similar radii. This road was actually built by loggers nearly 100 years ago. Zoom out to the extent of bookmark CR All 1:15,000 to see the final product. Turn off any labels not needed at this scale. Save the map once more. Acknowledgments Special thanks to Skagit County GIS for sharing its excellent imagery and terrain data and to the Chuckanut Ridge Homeowners Association and Skagit Fire District 5 for the opportunity to develop and test this model. The author thanks the staff and students at Bellingham Technical College for their help in testing and refining this workflow and to Esri Canada Limited's Vancouver office for the chance to present this exercise to a sample audience. www.esri.com Applying Turn Radius, Ft.lyr thematically maps turns and shows the tightest turns with thick red lines. 56 ArcUser Winter 2010