Interpreting Prairie Land-Cover Classes and Map Uncertainty

A prairie land-cover map is a set of educated labels, not a field survey. Before you use one to decide which grassland, cropland or wetland patches to look at, check four things: whether the map covers the area you care about, how the map defines each class, how coarse its cells are, and how accurate the class you care about is. The overall accuracy figure printed in a map's summary can hide large differences between classes, so the class-specific numbers matter most when you are choosing where to observe.

A worked example: Saskatchewan's Prairie Landscape Inventory

Saskatchewan's Prairie Landscape Inventory is a useful example because it publishes the details a reader needs. It maps the province's Moist Mixed Grassland ecoregion at 10-metre resolution using Sentinel-1 radar and Sentinel-2 optical satellite imagery. Its legend has seven classes: cropland, native grassland, mixed grassland, tame grassland, water, woody plants and urban area. The urban areas come from a mask based on Canada's Annual Crop Inventory 2020 rather than from the project's own classification.

This is a Saskatchewan product. It is a model for how to read a prairie map, not a source of habitat labels for Medicine Lake or anywhere else in Montana. For Montana ground, find a product whose stated coverage includes the area, then apply the same reading steps below.

Step 1: Confirm coverage and dates

Read the mapped area first. A map that stops at an ecoregion, province or state boundary says nothing about land outside it, even if the prairie looks continuous on the ground.

Then separate the dates. The Saskatchewan catalogue entry was modified on February 26, 2025, but that timestamp describes the catalogue record, not when every satellite image was captured. Grassland can be plowed, seeded or flooded between image capture and your visit, so record the imagery dates if the documentation gives them, and leave that field blank if it does not rather than substituting the metadata date.

Step 2: Read each class definition, not just the class name

Class names that sound universal are often defined for one project. In the Saskatchewan inventory:

• Native grassland: at least 75% native grasses.
• Tame grassland: at least 75% seeded or planted introduced species.
• Mixed grassland: a separate, heterogeneous class for ground that does not meet either threshold.

These thresholds belong to this project. Another map may label something "native grassland" using a different cutoff, different vegetation types, or a different source of reference data, so the same word on two maps does not guarantee the same kind of ground. When a birder cares about the difference between native prairie and planted cover, the definition is the part of the legend that answers that question.

Step 3: Understand what one map cell represents

Resolution sets the smallest unit the map can label. Illustrative calculation: a 10 m by 10 m cell covers 100 square metres. The whole cell receives one class, even if it contains a fence line, a small slough edge, a patch of shrubs and grass. The label is the classifier's best assignment for that cell, not an inventory of every feature inside it. Narrow features such as shelterbelts, ditch margins or the fringe of a wetland can be absorbed into neighbouring classes or show up as scattered single cells.

Step 4: Check overall and class-specific accuracy

Accuracy assessments compare map labels with reference sites whose true class is known. Two class-level measures are worth learning:

• User's accuracy: of the places the map labels as a class, the share that really are that class. It tells you how far to trust a label you see on the map.
• Producer's accuracy: of the places that really are a class, the share the map labeled correctly. It tells you how much of that class the map missed by calling it something else.

Measure	Saskatchewan inventory value	What it means for a reader
Overall accuracy	70.3%	About 7 in 10 validation sites, across all classes, received the correct label
Mixed grassland, user's accuracy	57.7%	Roughly 58 of every 100 validated sites labeled mixed grassland actually were mixed grassland
Mixed grassland, producer's accuracy	26.1%	Only about a quarter of true mixed-grassland validation sites were labeled as mixed grassland; the rest were mapped as other classes

The mixed grassland figures show why the overall number is not enough. A headline 70.3% sounds reasonable, but a reader searching specifically for mixed grassland would find a label that is wrong in a large share of cases and a class that is heavily under-mapped. Much of the real mixed grassland in the area sits under other labels.

Step 5: Turn a mapped patch into a field question

Once you have read the scope, definitions and accuracy, treat a mapped patch as a hypothesis about land cover. A practical sequence:

• Verify that the map's coverage includes the patch.
• Read the definition of the class assigned to it.
• Check the class-specific accuracy, if the map reports it.
• Record the patch as a mapped classification, not a confirmed habitat type.
• Write an observation question, such as whether the vegetation on the ground matches the class definition.
• Gather separate evidence for whether a species occurs there, whether the habitat is suitable for it, and whether you have legal access.

Illustrative example: a patch labeled mixed grassland on the Saskatchewan map, with 57.7% user's accuracy, is a reasonable place to ask "Is this a blend of native and planted grasses?" It is not evidence that a particular grassland bird nests there, and it is not permission to enter. Land cover, bird occurrence and access are three different questions, and the map answers only the first, with known error.

A map-reading worksheet

Recording these fields before a trip keeps map labels and field observations separate:

Field	What to record
Product and version	Name and version of the land-cover map
Mapped area	The stated geographic coverage
Imagery dates	Capture dates if documented; otherwise leave blank
Metadata date	Catalogue or record date, kept separate from imagery dates
Resolution	Cell size, such as 10 m
Legend code and definition	The class label plus its written definition and thresholds
Validation metrics	Overall accuracy and the user's and producer's accuracy for the class of interest
Patch of interest	Location described as a mapped class
Field question	What you intend to check on the ground
Access information	Ownership and permission, from a separate source

Used this way, a land-cover map narrows where to look and what to look for, while the weak spots in its accuracy table tell you where your own careful field notes add the most value.