calculate stream order for the arcs in a coverage.  Stream order is calculated as either STRAHLER or SHREVE.  The arcs must be oriented downstream for ORDER to work properly.



ORDER <cover> {order_item} {STRAHLER | SHREVE}




<cover> - the input arc coverage.


{order_item} - the name for the output arc item that will be calculated equal to stream order.


If {order_item} is not specified, it is named ORDER.


The {order_item} can be a new item, or an existing item.


If the {order_item} already exists, it must be a Binary or Integer item.


If the {order_item} already contains values, these values will be used as initial values.  You can use this to your advantage.  For example (using STRAHLER ordering), if your coverage has a main stem stream that originates upstream from your coverage and you know that this stream is a 4th order stream when it enters your coverage, then assign 4 to the first (i.e. upstream) arc of the main stem in your coverage.  Then run ORDER.  The 4 will be assigned to all arcs downstream from the first arc, until it joins with another 4th order stream, creating a 5th order, etc.


{STRAHLER | SHREVE} - how order is to be calculated.


STRAHLER - Headwater arcs are assigned an order or 1.  When two or more arcs of the same order converge, then the arc downstream of the confluence is assigned an order one greater than that of the upstream arcs.


SHREVE - Headwater arcs are assigned an order of 1.  When two or more arcs converge, then the arc downstream of the confluence is assigned an order equal to the sum of the orders of the upstream arcs.


NOTE: For both STRAHLER and SHREVE, when there is divergent flow (i.e.  a stream breaks into two or more downstream arcs, e.g. braids and deltas), then the downstream arcs retain the order of the upstream arc.  However, if the divergent arcs come back together, then the order of the arc downstream of the convergence will not be increased.





ORDER runs from the ARC module of ARC/INFO.


If the results aren't correct, it may be because one or more arcs in the <cover> aren't oriented downstream.  It may also be because there are break(s) between arcs.  In these events, correct the problems, recalculate the {order_item} to zero (or whatever the initial values should be), and then run ORDER again.


If there are break(s) between arcs that are meant to exist, you can overcome this by assigning the correct order to the downstream arc before running ORDER.  (See discussion under {order_item} in the ARGUMENTS section.)