Table of Contents

1. Introduction
2. Subdivision of Cells
3. Cell Threshold Statistics
4. System Design for Cells
5. What Use are Cells?

1. Introduction
Prominence Cells are a method of defining regions. For example, we can divide North America into 4 "cells", each one centered around one of the four mountains with 4000m of prominence. Below is a crude sketch of the four P4000 cells in North America:

The above map is derived because there are only 4 peaks in North America that have 4000m of prominence:

  Peak      Height  Prominence (m)
------------------------------
  McKinley  6194    6168
  Logan     5959    5250
  Orizaba   5640    4930
  Rainier   4392    4027 

Each peak defines a cell. The boundaries between the cells are the rivers which flow down from either side of the "key saddles" dividing the mountains. For example, the key saddle that divides Logan from McKinley is Mentasta Pass, and the rivers that flow from this pass are the cell boundary. To the south, the Copper River system flows to the Pacific Ocean. To the north, the Tok River flows into the Tanana, which flows into the Yukon River. The Yukon flows west to the Bearing Sea.

The rest of the boundaries are determined by tracing the rivers from the other key saddles. The separation between Orizaba and Logan is the rivers running down from the low point on the long ridge joining Orizaba to Logan, which is at Summit Lake Pass, just north of Prince George. From here the Peace, Slave and Mackenzie Rivers flow north, and the Fraser flows south.

The remaining boundaries are defined by the key saddle or Rainier, (Armstrong Pass) which is the low point on the ridge between Orizaba and Rainier.

Note that once a given prominence threshold is chosen, everything else is completely mechanical. You just find the key saddles, and trace the rivers.

  In Bivouac, we picked 500m as the basic threshold, because it corresponds to groups of mountains that are typically relevant to a given trip. North America breaks into about 4000 such "cells".

2. Subdivision of Cells
Previously we have only discussed a single level "cell map". However, we could also define a 2 level cell map by defining a lower level prominence threshold. For example, we could have a map divided into P4000 cells, and each of those cells could be subdivided into P3000 cells. For example, the Logan P4000 cell contains the following P3000 cells:

                  Height  Prom
---------------------------------
   Logan          5959    5250
   Blackburn      4996    3546 
   Fairweather    4671    3956
   Lucania        5226    3046
   Saint Elias    5489    3429  
   Waddington     4019    3289

The boundaries of the P3000 cell are the passes and rivers that separate it from other P3000 cells. Note that there is both a Logan P4000 cell, and a Logan P3000 cell. The P3000 cell is much smaller, because it is bounded by the nearest P3000 peak.

As with the top level cells, sub-cells are defined strictly by the key saddles of the lesser peaks. So to subdivide Logan 4000, one simply looks up the key saddles of each of the P3000 peaks within (except Logan itself). Their key saddles are guaranteed to be within the parent cell, because by definition all those peaks "go to" the high point of the parent. Fairweather goes to Logan, Blackburn goes to Logan, etc.

Here are some of the P3000 boundaries for Logan4000. The Fairweather key saddle is Champagne Pass, so two boundaries are the Alsek River and the Yukon River. Saint Elias key saddle is Columbus Glacier, which runs in both directions down to the ocean. Lucania's key saddle is the Hubbard-Logan glacier. The Hubbard runs down to the Gulf of Alaska and forms the boundary between the Fairweather cell and the Lucania cell. And so on. To subdivide any given cell, one simply identifies the peaks that are over the prominence threshold, and find their key saddles. The rivers/glaciers draining these saddles will form the boundaries.
 

3. Cell Threshold Statistics
Now that you know what a cell is, here is how the Bivouac website implements cells.

In setting up any given cell hierarchy, the only thing that is arbitrary is the threshold levels. For bivouac, the top level are the 4000m cells (4 cells). These are divided into 3000m cells. There are only 12 such cells, so each top level is subdivided into an average of 3 cells. The next level is the 2000m cells, of which there are 81. This means each 3000m cell is divided into an average of 8 cells. Here is a summary:

 Threshold  NumCells  Average
-------------------------------
  P4000      4         
  P3000     12          3
  P2000     81          9
  P1000   1120         13
  P500    5101          5

Note that unlike our "regions", the number of subdivisions in a cell can vary quite wildly. For example, although the average number of subdivisions in a P1000 is 5, they can range from 1 to 25, as shown below: (Use Queen Bess 2000 to get this list:)

  P1000    Number of P500s
----------------------------
  Queen Bess    2
  Addenbroke    1
  Albert        1
  Alfred       20
  Ashlu         4
  Birkenhead    1
  Blackfin      1
  Boardman      5
  Bunsen        1 
  Taseko       15
  Good Hope     3

And you can see that there is the same wide variance in the Rockies: (use Columbia 2000 to get a list)

  P1000      Number of P500s
----------------------------
  Columbia    10
  Brazeau     25
  Clemenceau   5  
  Cline        4
  Dias         2
  Forbes       8
  Frigate      6
  Lyell        5

4. System Design for Cells
Now that you know what we mean by "cell", here is how we implemented them in Bivouac.

Cell Hierarchy on Mountain page First of all, every mountain page now shows the hierarchy of cells that contain the peak. For example, look up Mount Garibaldi, you'll see the following:

  Logan4000/Waddington3000/Wedge2000/CastleTowers1000/Garibaldi500

These "cell hierarchies" are the same idea as the previous "region hierarchies". Think of each low level cell as a mountain range. If you click on the lowest level (Garibaldi 500), you see the mountains immediately around Mount Garibaldi:

   Atwell Peak
   Dalton Dome
   The Tent
   The Sharkfin
   Glacier Pikes
   ... 

   Castle Towers P500
   Black Tusk P500
   Garibaldi P500

One useful thing about displaying the hierarchy of cells for any given peak is it immediately puts the peak in context, much better than the line parent. For example, if someone mentions "Mount Vic", you may never have heard of "Beece Peak" or even "Taseko Mountain". But you MUST have heard of one of the cells below:

  
Logan 4000/Waddington 3000/Queen Bess 2000/Taseko 1000/Vic 500

Multiple Nested Cells Note that for a really high prominence peak, the cell hierarchy may contain the same name several times. For example, look at Mount Robson:
 

 Orizaba 4000/Whitney 3000/Robson 2000/Robson 1000/Robson 500

Cell Guidebooks: Each of the thousands of "Cell Pages" provides a link to a "guidebook" for that cell. The guidebook lists all the peaks that fall within the cell. These guidebooks are ideal to print out if you are going into a given area, and want details on all the subpeaks, etc. you may be able to climb. For example, when going into the Petlush area, you'll find an ideal list of other little peaklets you can climb while you are there. Most 2 or 3 day trips are confined entirely to one P500 cell. Printing out the cell guide is much more useful than a radius guide, because the area can be quite irregular. Radius guides tend to include irrelevant peaks which are separated by huge drops.

There is a link to the "P500 guidebook" on every mountain page more than 500 meters prominence. For lesser peaks, click on the lowest level of the hierarchy, and then click on "cell guide".

5. What Use are Cells?
Cells are useful for the following:

 1. To provide useful guidebooks for areas with no mountain ranges
 2. To immediately provide context for unknown peaks

Guidebooks: Every P500 mountain, and every P500 cell page has a link to the corresponding P500 Cell Guide for that peak. This guide lists the mountains that fall within that cell. These are really useful little guides to run off when you are going into the area of a specific peak, because it lists all the subpeaks, and related peaks. This requirement provided the original inspiration for cells. The Radius guides are often not as useful because they contain all sorts of peaks that are separated from the area you are in by a huge gorge. For example, a suitable radius of guide for the Rainbow range might be 30 km radius. However, such a guide will contain dozens of irrelevant peaks that are separated from the Rainbow range by the deep gorge of the Bella Coola river, and which would only be relevant to a completely different trip. However, by running off several P500 guides for Tsitsutl and Beef peak, you will end up with a much more compact guidebook.

Context The hierarchy of cells printed at the top of every mountain page allows you to understand the location of a peak. For example,

Meaning of region understoodThe advantage of cells over the region boundaries is that they are self defining. Assuming you know the terrain, and understand what P500 means, you can immediately grasp what sort of area is probably covered by something like the Waddington P500 cell. Readers of this Page

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