Bottleneck Analysis

Summary

Finds the route through a corridor polygon between two wildland blocks that maximizes the minimum corridor width encountered — the route with the widest bottleneck, chosen over every strand and branch of the corridor at once — and measures the corridor width at regular stations along it. A narrow spot is a bottleneck, and for species sensitive to edges or development a severe bottleneck can make a corridor useless; this analysis shows exactly where the corridor narrows, by how much, and for how long. Compare the narrowest point against what your species tolerates — and where a pinch is not constrained by hard edges, that is where widening the corridor buys the most. A modernized port of the CorridorDesigner Evaluation Tools' Bottleneck Analysis; no Spatial Analyst needed.

Provably the widest available route

The corridor's medial axis — its skeleton, where every point is the center of a circle touching the boundary on two or more sides — is computed exactly in vector from a Voronoi construction, with the local corridor half-width known at every point. The route through that skeleton maximizing the minimum width is found over all strands and branches simultaneously, so the answer is exact — no raster approximation, widths and lengths in meters. An optional width threshold classifies the route into above- and below-threshold stretches.

Window and geoprocessing tool

The interactive window is where the exploration happens: run the analysis, then drag the width threshold and watch the statistics, the width-profile graph, and the highlighted sub-threshold stretches update live; place the graph on a layout when it tells the story. The geoprocessing tool runs the same underlying analysis as a scripting and batch surface — ModelBuilder chains, many corridors in a loop — and produces the same three outputs: the route polyline, optional station points with widths, and optional above/below-threshold segments, each carrying the analysis record. What the geoprocessing, ModelBuilder and Python scripting options do not include is the window's interactivity: no live graph to drag a threshold on, and no way to place a graphic or a statistics text element on a layout — those belong to the window alone. Run it once per threshold you care about, and use the window when you want to explore.

A tour of the window

The example below continues the black bear corridor from the Corridor Design Tutorial and the Corridor Evaluation Tutorial.

Corridor and blocks

The corridor polygon must be a single polygon: the tool finds one best route, and a corridor made of several disconnected strands (common straight out of Least-Cost Corridor, whose slices can sprout branches) has no single answer. Here that means picking one strand out of the black bear 2% corridor — the wider one running south through Tumacacori — rather than handing the tool every strand at once.

The status text beside each Browse button confirms what the tool sees: Single polygon in blue when a field is ready to run, or a count in red when it is not.

The two wildland blocks are usually two features in the same feature class, which is exactly the case here: both Wildland Block A and Wildland Block B point at the same Wildland Blocks layer. The tool notices there is more than one feature and asks you to narrow each field down to one, with a live count: 2 Polygons in Wildland Blocks: Select 1. The SQL... button beside each field opens the same query builder used throughout the add-in, so you can pick the block by an attribute rather than by selecting it on the map first.

With both blocks resolved to one feature each and a width threshold typed in, click Run Analysis.

Reading the result

The graph plots corridor width against distance along the route; the statistics panel on the right reports the route length, the narrowest point and where it falls, and the mean, median and standard deviation of width along the whole route. With a threshold set, both the graph and the statistics split at that value: the graph colors the profile blue above the threshold and red below it, and the map does the same to the route line, so a glance at either one shows where the corridor is comfortable and where it pinches.

Adjusting the threshold

Change the threshold by typing a new value, clicking a point on the graph, or dragging the dashed threshold line itself up or down — no need to rerun the analysis, since the width profile was already computed once and every number and color below the line simply reflects wherever it now sits. Suppose, after seeing the 2,000 m picture, you decide that 2,000 was too cautious and the corridor really only becomes a problem below 1,000 m. Move the threshold down and the story changes completely: only 6.9% of the route now falls below it, in two short stretches instead of four long ones.

Advanced options

Three controls, tucked under the Advanced expander, tune the analysis without changing what it measures:

• Stations — how many points along the route the width is sampled at (default 1,000). More stations trace the profile more finely; the default is enough to catch a bottleneck a few meters wide on a corridor several kilometers long.
• Boundary sampling (m) — the spacing used when building the Voronoi skeleton from the corridor boundary. Left blank, the tool picks a spacing scaled to the corridor's own size (the extent diagonal divided by 2,000). A finer spacing traces a more detailed boundary at the cost of a slower run; it rarely needs to be set by hand.
• Simplify tolerance (m) — simplifies the corridor boundary before analysis. Blank means automatic, 0 means no simplification at all. A boundary with a great many vertices (a corridor sliced from a fine-resolution raster, say) can be simplified without changing the medial-axis answer in any way that matters, and the run finishes faster for it — the same trade the Patch Analysis tool offers for the same reason.

The Show route on map checkbox controls only whether the route and its colored stretches draw as a temporary overlay while you work; it has no effect on the analysis or on what you can save afterward.

Getting results out

Six buttons along the bottom of the window cover every way to keep what the analysis produced:

• Save Route..., Save Points..., Save Segments... write the route polyline, the width-measurement stations, or the above/below-threshold pieces of the centerline to a real feature class — the map view shows everything in-memory until you do. Save Segments is the one behind the colored route in the layout figure below.
• Copy Stats puts the statistics panel on the clipboard as plain text, ready to paste into a report or an email. You can also select text directly out of the panel with the mouse and copy just the lines you need, the way you would from any document.

  

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  Save Graph... exports the width-profile graph as a PNG image or an SVG vector file, for a report or presentation that is not built as an ArcGIS Pro layout.
• Add Graph and Stats to Layout places the graph and the statistics on a layout together, as native, individually editable graphic and text elements — not a picture. If a layout is the active view, it goes there directly; otherwise you are asked which of the project's layouts to use, or, if the project has none yet, pointed to Insert ▸ New Layout.

The geoprocessing tool, and ModelBuilder

The geoprocessing tool takes the same inputs as the window — a corridor polygon, the two wildland blocks (with the same per-field SQL expressions when a layer holds more than one feature, as in the black bear example above), and an optional width threshold — and writes the route, the station points, and the above/below-threshold segments directly to named output feature classes, no window required. The advantage of this version of the tool is that it can be run from a Python script or chained into a string of tools in ModelBuilder, so one model can evaluate every corridor in a project the same way. The downside is that you cannot easily explore the consequences of different thresholds, since each threshold is a separate run rather than a drag on a live graph, and you cannot create graphics for your layouts or reports; both of those belong to the window.

Parameters (geoprocessing tool)

The dialog lists one more parameter, Profile JSON path. It is used by the Bottleneck Analysis window to receive the width profile and should be left blank.

Python

import arcpy
arcpy.ImportToolbox(r"C:\path\to\JennessEnterprisesTools.pyt")  # your install path
arcpy.jenness.BottleneckAnalysis(
    corridor=r"D:\corr.gdb\bear_2pct_corridor",
    block_a="Tumacacori_Block", block_b="SantaRita_Block",
    threshold=1000,
    out_route=r"D:\corr.gdb\bear_bottleneck_route",
    out_points=r"D:\corr.gdb\bear_width_stations")

Recommended citation

Credits and references

By Jeff Jenness, Jenness Enterprises (www.jennessent.com), ported from the CorridorDesigner Evaluation Tools by Jenness, Majka and Beier.

• Beier, P., D. Majka, and J. Jenness. 2007, revised 2026. Designing wildlife corridors with ArcGIS: ArcGIS Pro edition. Workshop book, revised by J. Jenness for the Corridor Designer Tools of the Wildlife and Forestry Tools add-in. Available at: CorridorDesigner_WorkshopBook_2026_ArcGISPro.pdf (5 MB)
• Jenness, J., D. Majka, and P. Beier. 2014. CorridorDesigner Evaluation Tools. Available at: corridordesign.org (archived copy at the Internet Archive)

Licensing information

Works at every ArcGIS Pro license level (Basic, Standard, Advanced). No extension licenses are required.

Related tools and pages

• Corridor Evaluation Tutorial — Metric 2 in the evaluation workflow.
• Patch Analysis — the gap question to this tool's width question.
• Centerline and Width — the general-purpose medial-axis relative in the Geometric Tools.