Segments and Assignments

in this lesson

This chapter goes beyond the initial hasty period and looks at starting to subdivide, or segment the terrain using the mapping tools in SARTopo. At the end of this lesson, you should be able to do the following:

  • Define segments and assignments.
  • Draw effective and clean segments on the mission map.
  • Evaluate segments for size, access, and travel.
  • Gain efficiency in the planning process through using bulk ops.
  • Organize segments and concepts using folder and op periods.
  • Assign segments to teams based on priority and resource availability.

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What are Segments and Assignments?

Searches hinge on geospatial information that often requires more specific information than "the south side of the peak" or "area bounded by the Gordon Mill trail, Timberview trail, and the big ridge". Dividing the map into segments provides us with a geospatial alphabet that makes this communication easier - both when prioritizing efforts during the planning process, and when tasking search teams.

While there are many different approaches to naming search segments, this training will stick with our recommended best practice of using segments and assignments.

A segment is a line, buffer or polygon on the map, identified by a pair of letters (AG, DB, etc). Segments are created early in the planning process without regard to prioritization or search tactics, to give the planning team a broad geographic alphabet when talking about the search problem. Once created, segment boundaries and identifiers should generally not change throughout the duration of an incident. Despite the name, segments are still tracked on CalTopo as "assignment" objects, rather than plain lines or polygons.

An assignment is a segment that has tactics (e.g. resource type, team size, desired POD) added to it, and is identified by a number in addition to the segment letter. Generally, only segments that are intended to be searched in a given operational period are given numbers and referred to as assignments. We recommend tying assignment numbers to the operational period, e.g. 201, 202, 203, etc for OP 2 assignments.

This system allows you to create a large number of segments upfront, and then filter and prioritize them as part of your planning process. Having a catalog of segments to fall back on also makes it easy to pivot the search in response to new information, or redeploy teams in the field. It also keeps individual task identifiers unique, so that you don't have multiple days' worth of debriefing and tracks in the same area, reusing the same name. There will always be edge cases, such as sending both dog and ground teams into the same segment on the same day, but we have found this approach to work well on large, complex .

This is a map with lettered segments drawn on it.

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Preparing for Drawing Segments

Good segments generally follow a few simple rules:

  • Appropriate Size: Searchable by a team in a day.
  • Navigable: Bounded by visually-identifiable features such as streams, ridges, or trails - or if necessary, elevation contour lines.
  • No interior boundaries - if a segments spans both sides of a creek, teams should be able to easily cross that creek.
  • Consistent Detectability and Probability: Where possible, consistent detectability (ie vegetation density) and probability (ie likelihood of the subject being in a given location) across the entire segment.
  • Clean and complete: avoid gaps and lines that don’t make sense.

The size, type and location of segments that get placed on a map are going to depend on more input from the planning team, including:

  • Segmenting linear features vs relying only on area segments.
  • Segment size - higher POD searching generally requires smaller segments.
  • Subject's expected travel distance from the PLS.
  • Subject's expected direction of travel.
  • Deductive search area determinations, such as boundaries the subject is unlikely to cross.
  • Likely locations based on additional evidence, such as cross-referencing cell phone data with viewshed analyses (link).
  • Areas of high natural hazard (creek crossings in spring, avy terrain, steep cliffs, burn scars with standing dead trees) that might get marked as independent segments for safety reasons.

Expected travel distance may vary with terrain.

Drawing Segments

We recommend approaching segmentation as a 3-step process, all using the "Assignment" object type:

  • Start with lines drawn on linear features
  • Convert those lines to buffers
  • Fill in the surrounding areas with area polygons

We recommend starting with lines because once drawn, buffers are treated the same as polygons - unlike lines, there is no way to go back and split a buffer in half, or join it with another buffer. Draw a line while using snap-to to follow linear objects like roads, trails, or creeks. As you draw the line, you will see the distance you have drawn so far in the upper right hand corner. If you are snapping, move the cursor off of the snap object in order to see the distance.

For a hasty-style search, lines may be sufficient. For larger searches with area polygons, buffers provide visual clarity that prevent the segment from being lost in the border between two polygons. To generate buffers, use the “copy to” function to copy the lines to buffers. If you are satisfied with the copied buffer, you can go back and delete the original line, or put it in a hidden folder for later.

Note: using “convert to” in place of “copy to” will eliminate the original object. If you make a mistake during the conversion, you’ll have to start over. Use copy, then delete the original object when you have the new one right.

Here are a selection of area assignments. In the next section we’ll look at why they are the shape they are.

The task of drawing assignments can be split among several people, so long as the planning team clearly communicates the goals and requirements.

Exercise #8

For this exercise, you will focus on drawing only a few area segments to start as opposed to segmenting out the entire search area as you normally would. Draw 3 area segments using assignment type objects on your search map. Letter these segments as BA, BB, and BC in the letter field for each object. At this point, do not fill in any other assignment information.

The purpose of this exercise is not for you to choose the “best” segment locations, but rather to practice drawing the objects using the strategies mentioned above.

Grading Criteria:

Grading Criteria:

  • There are 3 area assignments lettered BA, BB, and BC.

Reference Links

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What makes an effective segment and assignment?

The goals for drawing effective and clear assignments are that they are an appropriate size, relatively easy to understand and navigate, and are clean and don’t leave areas empty.

  • Appropriate Size: The segment should be searchable by a team in one day. The amount of time available, the size of the ground team, the type of terrain they are covering, and the level of detail for the search goals (POD) are all determining factors for defining an appropriate sized segment. Experience has shown that assignment areas should not be much larger than 60-120 acres. To quickly measure the size of a line or area segment, hover your mouse over it and view the area in the upper right of the map viewer, or click on it on the map. The popup will show the area. Additionally, you can use bulk ops to quickly see the area of multiple assignments. How might you change the size of the segment for a detailed grid search? How about for a helicopter assignment? An OHV assignment?

Go to the Dragontail search map (SUG9) and measure some of these assignment areas. How many acres are they? Are the areas similar to each other? Is one much larger or smaller than the others?

  • Navigable: Screen time on mobile devices and GPS units drains the battery much faster than leaving the screen off. Using boundaries that can be visually identified in the field reduces searchers' reliance on GPS, and also tends to create easily-traversable assignments. Natural features such as ridges, cliffs, creeks or drainages, treelines, and meadows make great segment boundaries, as do manmade features like roads, trails, powerlines, canals, or railroads. Contour lines are also useful segment boundaries because once the searcher navigates to the appropriate elevation, they can traverse at more or less the same elevation fairly easily without constantly referring to a navigation tool. Segments also should be navigable within their boundaries. For example the segment should not be split in half by a cliff face with no way through it on foot.

    Additional comments about navigability:

    • Square or rectangle segments might make sense in an urban setting, such as the dementia patient scenario, but are not navigable in a wilderness situation. In the overdue climber scenario, having repeated identical segments might make the lives of your ground searches more difficult than they need to be, and will certainly drain their phone battery as they continuously reference their location.

    • When creating segments for other types of resources, you may need to consider other factors and change how you draw segments. For example, an air assignment will need large and obvious landmarks to define their zone. Ridgelines or large creeks and rivers are usually good indicators, but a trail might be hidden from the air. For an OHV or mounted assignment, put segment boundaries at intersections or a high point on a road, not in a random position in the woods with nothing that will stand out to the searcher.
  • Consistent Detectability and Probability: If half off a segment is wetland and half is open scrubland, that makes prioritization and timing difficult. Try to keep segments relatively consistent throughout the area.

  • Clean and complete: Finished maps should be clean with boundaries matching up to each other and limited undefined holes between segments. Our goal is to communicate what needs to be done and not leave things up for confusion in the field.
    • Use snap-to set to “lines” to match one assignment up to another.
    • There are of course exceptions: we may want to leave a steep area of cliffs out from our final assignments. These areas can be called out as hazards or no-search areas on the map to prevent confusion.

Exercise #9

Evaluate the 3 segments that you just drew on your map for Exercise #8. Determine if each segment is:

  • An appropriate size?
  • Relatively easy to understand and navigate?
  • Clean and does not have any gaps between it and the neighboring segments?

Edit or delete and redo any segment(s) that do not meet one or more of the above criteria. For these three segments (BA, BB, and BC), edit the assignment description text and add the size of your segment, and why you chose the boundaries that you did.

Next, add 7 additional segments, keeping the criteria for good segmentation in mind. Letter these as CA through CG. Your goal is to have a map with properly sized segments that are easy to navigate and fit neatly together.

Grading Criteria:

  • Segment BA, BB, and BC are an appropriate size, follow ground features indentifiable to a field searcher, and are cleanly drawn.
  • Snap-to was used to make segments line up to each other and/or to trails, roads, water, etc.
  • There are 7 additional segments drawn on the map that also meet the expected criteria.

Reference Links

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Lettering and Relettering

While each assignment object contains many data fields, at this time all that is important is the lettering. Other data fields are useful later, after the segments are drafted.

Add a letter sequence as you create the object. For most missions, we like to use 2 letters in sequence - the first indicates a division if you have them, and the second is the assignment within that division. Starting at the end of the alphabet for line assignments, and at the beginning for area assignments to help avoid confusion. For example, most missions will start with line assignments AZ, AY, AX, and area assignments AA, AB, AC, etc. As you add divisions or reach the end of the alphabet, you can add BA, BB, BC, etc


Let’s say you have multiple mappers drawing assignments and accidentally end up with two segments designated AR. You can quickly re-letter all or a selection of segments using bulk ops.

Sorting by size will help you identify area segments (in acres) from line segments (in miles). Here we multi-selected all of the area segments except for the very large air-ops segment.

Next, we scrolled down through the bulk ops box to get to “reletter”, then chose to start lettering from AA. Upon completion we got all area segments lettered in order from AA to AM.

The order of assignment letters does not matter so much compared to ensuring that each segment has a unique letter code, and that once a segment has a letter code that it doesn’t change during the mission. (IE if you deploy teams to area AA during OP2, don’t rename the same area to AY during OP3. This creates confusion for searchers and search managers.)

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Adding Details

Many segments will have duplicate information in them; for example, team size, which radio frequencies are in use, assignment descriptions, transportation methods, and priority level. These can all be edited at once using bulk ops.

You only need to fill out the fields that are relevant for your team and the mission. There are no required fields for the object to work. However, when we get to producing IAP and assignment forms, these fields will populate automatically to the forms you create. They also will be available to users via the CalTopo App, where they can read their assignment details in the app directly.


Prioritizing search segments for assignments depends on many factors, most of which come from the subject’s history and intended route. Sometimes you are not familiar with the details of the search area on the ground, or you have little information about whether the subject’s intended route matches with reality. Taking a look at the CalTopo shared maps layer, you can get a sense of where other people tend to go. In especially heavily used areas, you can narrow the content selection by choosing “tracks only” or “popular maps” from the dropdown menu. The tracks-only option might be the most helpful because you will see where people truly end up going, rather than just what they plan to do.

Exercise #10

To practice using bulk re-lettering, open bulk ops, select segments CB through CG and reletter them starting with R. You should get RA through RF.

Grading Criteria:

  • Segment CA still exists (lettering not changed.)
  • 6 Segments are labeled RA-RF.

Reference Links

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Team Numbers

Recall that we use a single set of segments to cover multiple operational periods to avoid confusion. To achieve this, we recommend reusing the segment area letters, and changing the team number to reflect the operational period. Teams can be numbered by op number then team number. So, if segment AD were assigned to team 05 in OP2 and to team 03 in OP3, it would be labeled AD 205 in OP2 and AD 303 in OP3.

If re-assigning a segment for a second or third OP, in the assignment description field, the old description gets moved to “previous efforts” and adjusted to reflect the actual efforts, and the description is updated to the current assignment description.


To add numbers to a bunch of segments at once, use the renumber function in bulk ops. The renumber function will let you designate a starting number and populate the assignments that you select for the op period with a number. Select all the assignments that you want to put teams into for that OP, select renumber, and enter a number to start with. For example, if you are preparing OP 2 and you want to put teams into 6 segments, select those six from the list using shift or ctrl/cmd to select multiple items from the list, choose “renumber” and set the number at 201. You will get numbers from 201 to 206.

Use the column header for Op Period in the bulk ops window to group all your op periods that you’ve chosen for the day together. Select them by using holding the shift button and selecting the first and last in the list that you want to renumber. Scroll down and select “renumber”.

Enter a starting number.

Segments now have numbers associated with them and are ready to go to field teams.

Exercise #11

Given the available resources for OP2 (shown below), decide which of your existing segments will become assignments for the next operational period (OP2). Use the renumbering function to assign field team numbers to some of your segments that will get used in OP2, based on how you can logically distribute your availabe resources.

For example, you may choose to divide your searchers into three groups of 3 and assign them to three segments, and assign the dog team to a fourth segment. In this case, you should end up with 4 segments that have numbers. The numbers should start with 201 to indicate OP2, Team 1, and go up from there.

Resources Available for OP2:

  • 9 ground searchers
  • 1 trailing canine team with a trailing dog, handler and helper

Recall that segments become assignments when you add (assign) teams to them. Segments are usually sized for a ground team of 2-5 searchers to cover in one operational period. You can indicate the number of searchers/personnel for an assignment object by editing the object.

Grading Criteria:

  • A selection of segments has been converted to assignments with team numbers added, starting with 201.
  • Assignments are chosen appropriately for 9 ground searchers plus one dog team.

Reference Links

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Organizing Segments and Assignments using Operational Period Map Objects

Keeping segments and assignments organized as you move through past the hasty period and into multiple operational periods OP2 is crucial. Starting early with good organization practices will save you a lot of time and headaches later. To this end, we have two primary tools to help with organizing: Op Periods and Folders. We’ll focus on Op Periods in this chapter, and cover folders in subsequent chapters.

Operational Periods

An Operational Period (OP) is a map object that does not display on the map. It is an organizational tool. Once you create an OP, you can link an assignment to that OP. Then you can sort or display segments by OP.

Traditionally we use names such as OP1, OP2, etc, but it may be useful to expand the nomenclature to include OP2 Air, OP2 Ground, or an op called “staging” that stores segments that are not in use.

Your segments do not need to be tied to Op Periods. When you convert segments to assignments, you can tie them to an op period.

Let’s take a look at the WA mountaineer example to see how we can start using Op Periods to organize the segments drawn there. First, I’ll make an operational period object called Segments, and use bulk ops to tag all of the existing objects in the assignments folder as the Segments Op. I’ll set the op period color as green for demo purposes.

Here we can see that there is a new folder called “operational periods” containing the Segments OP, which is set to green. All the assignment objects are now tagged as belonging to the Segments OP, and thus are green.

Now imagine that we are choosing assignments for OP2. I’ll create OP2 as a new segment, then select several of the assignments to use for OP2 and change the OP period attribute for those, either with bulk ops or by editing each object.

OP2 (blue) now has some assignments tagged for it. The unused segments for OP2 remain green and tagged as segments. They are ready to be converted to assignments if needed, say if 20 extra searchers show up.

Exercise #12

Add an operational period for OP2 to the map. In the previous exercise you chose segments and gave them numbers based on the available resources. Now, use Bulk Ops to change the Operational Period for those segments to OP2. Now you have assignments for OP2.

Grading Criteria:

  • OP2 Map Object Exists
  • Numbered assignments from Exercise 11 are designated as belonging to OP2.

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You have now segmented your search map into areas for assignments or other useful designations such as hazards. You drew clean assignment boundaries, and considered terrain, ingress and egress, size of the area, and obvious hazards. You re-evaluated all your segments and redrew any that were too big or too small. You used op periods to sort assignments and created folders to help organize air assignments or other resource types, or specific areas that you are not using as assignments.

Now you should be ready to prepare for team deployment. The next chapter will look at creating sections of your IAP and assignment maps from what you developed for your assignments.

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