The Reference Polygon

Updated April 15, 2025

Introduction

A history stack documents the changing shape of a plant population over time. A history stack may have many observation records in it, and some or all of those records may have an associated polygon.

In Plant Observation Entry (POE), it is possible to choose which one of these polygons best represents the population — the chosen polygon is called the reference polygon.

When there are many populations of the same weed in an area, using reference polygons can help to visually differentiate those populations in applications such as POE, Plant Distribution, and Group Observations.

An Example Reference Polygon

mg71897 is a record of Cortaderia jubata from Marin County Parks made in 2018. It is the most recent record of a history stack that has eleven records in it. The oldest record, or root record of the stack, is from 2004.

The reference polygon for this stack has been assigned to the polygon associated with mcp2701 made in 2015.

When you are viewing mg71897 (the 2018 record) in POE, open POPULATION and check

Show the reference polygon on the map

and you will see the reference polygon (blue) superimposed over the record’s own polygon (red). In this case, it appears that the area occupied by this population has shrunk between 2015 and 2018.

How the Reference Polygon is Used

Plant Observation Entry
In Plant Observation Entry (POE), if you want to see nearby records of the same plant, open History and press .

For each nearby population, POE shows only the most recent record. If that population has a reference polygon, then the reference polygon is displayed. Otherwise, if the most recent record has a polygon, that polygon is displayed.

Plant Distribution
In the Plant Distribution application, zoom in close and check Polygons.

For each population in the map area, Plant Distribution shows only the most recent record. If that population has a reference polygon, then the reference polygon is displayed. Otherwise, if the most recent record has a polygon, that polygon is displayed.

Group Observations and Multiple Group Search
To see reference polygons, open Symbology and check both lines / polygons and use reference polygon. If you combine this option with the History criterion Only the most recent, you will see one record per history stack, with the reference polygon displayed for those records that have a reference polygon.

If you save a search that includes this option, and then use that search to load historical records into the phone app, you will be able to see observations with their reference polygons in the phone app.

More Information

Weed Manager Design: The Population Record

Plant Observation Entry Help