Explanation of Data Measurement Exercise

Exercise Objective

Exercise Explanation

1. Open, view, and zoom. With ImageJ running, and the map open, the Magnifying glass zoomed into the scale bar as shown in the first image on this page.
2. Trace scale. Using the ImageJ Straight line selections (5th button from left) tool the scale bar is traced by holding the left mouse button down and dragging the mouse.
3. Set scale. Using the ImageJ Menu > Analyze > Set Scale... option the scale is set by entering the "Known Distance" of 0.5, and the "Unit of Length" as km, as shown in the lower image on this page.
4. Focus on river. Using ImageJ, the image is sized to focus on the river by right clicking on the Magnifying glass and Scrolling tool hand.
5. Trace river. Using the ImageJ Segmented line selections tool the river length is traced. At the end of the river, double left click to end the selection.
6. Measure river. Using the ImageJ Menu > Analyze > Measure (Ctrl+M) the river length is read as about 0.9 km, as shown in the lower image on this page.
7. Focus on watershed. Using ImageJ, the image is sized to focus on the watershed by right clicking on the Magnifying glass and Scrolling tool hand.
8. Trace watershed. Using ImageJ Polygon selections or Freehand selections tool (3rd and 4th buttons from left), the watershed can be traced. Drag the cursor perpendicular to the Elevation contours.
9. Measure watershed. Using the ImageJ Menu > Analyze > Measure (Ctrl+M) the watershed area is read as about 1.0 sq km, as shown in the lower image on this page. A detailed outline of the watershed is shown on this link.

Image courtesy of USGS