> what is the distance (total length) of the selected lines? (using ArcMap)
From the ArcGIS Desktop Help, length, calculating for lines in the Index.
Click Editor on the Editor toolbar and click Start Editing. You can make calculations without being in an editing session; however, in that case, there is no way to undo the results. Right-click the shapefile layer you want to edit and click Open Attribute Table. Right-click the field heading for length and click Calculate Values. If there is no field for length values, you can add a new field for length by clicking the Options button and selecting Add Field. However, to add a new field, you need to exit the editing session. Click Calculate Values. Check Advanced. Type the following VBA statement in the first text box:
Dim dblLength as double
Dim pCurve as ICurve
Set pCurve = [shape]
dblLength = pCurve.LengthType the variable dblLength in the text box directly under the length field name. Click OK. Tip: The property length returns a field type of double. For best results, your length field should also be a double field type.
there is also an ArcObjects? developer Measure Tasks tool to do this:
" This sample allows you to measure the distance between locations using the sketch tool. The functionality in this example mimics the functionality of the Measure Tool, but it has the added advantage of the Editor's snapping environment. Use this edit task when you want to snap to the locations you are measuring from."