An inset map is a smaller, separate map placed inside or alongside a larger main map. It serves one of two purposes: showing a zoomed-in detail of a specific area, or showing a zoomed-out view that helps you understand where the main map fits in the wider world. You’ve likely seen one without knowing the term, such as the small box on a U.S. map that shows Alaska and Hawaii off to the side, or a close-up of a crowded downtown area pulled out from a city map.
The Two Main Types of Inset Maps
Inset maps fall into two categories, and they do opposite things.
A detail inset zooms in. It takes a small, cramped area on the main map and blows it up so you can actually see what’s there. The classic example is a map of the entire United States that includes a separate close-up of the New England states. At the scale of the full U.S. map, states like Connecticut and Rhode Island are tiny and their labels overlap. The detail inset solves this by showing that region at a larger scale where everything is legible. City maps use the same approach, pulling out a dense downtown core into its own mini-map so individual streets and landmarks are visible.
A locator inset zooms out. It’s a small overview map that shows where the main map’s area sits within a broader region. If the main map covers, say, a national park in Montana, a locator inset might show a tiny rectangle on a map of the western United States so you can immediately place that park geographically. A map of Corsica, for instance, might include a small locator showing the island’s position relative to mainland France and Italy. Locator insets are especially useful when the main map covers an area that isn’t immediately recognizable on its own.
Why Inset Maps Exist
Every map involves a tradeoff between coverage and detail. A map that shows a large area can’t also show fine detail without becoming enormous. Inset maps let cartographers cheat that tradeoff by running two (or more) scales on the same page.
For navigation, this is practical. A hiking map might dedicate its main space to trail routes, then include a locator inset showing the broader region with roads and towns so hikers can orient themselves. A regional road map might use a detail inset for a metropolitan area’s street network, giving drivers the close-up view they need without requiring a separate map entirely. This is especially helpful for people who aren’t experienced map readers, since the inset provides immediate geographic context that might otherwise require flipping between multiple maps.
Inset maps also handle noncontiguous territories. When mapping the United States, Alaska and Hawaii can’t appear at their true geographic positions without making the map absurdly wide and mostly ocean. Placing them as insets (usually in the lower left corner) keeps everything on one page, though sometimes at a different scale than the continental states.
How Inset Maps Are Designed
Good inset maps follow a few visual conventions that help you read them correctly. The inset is visually separated from the main map using a distinct border, a drop shadow, or both. This prevents confusion about where the main map ends and the inset begins.
The connection between the inset and the main map needs to be obvious. Cartographers handle this in a couple of ways. One common method is a caption like “Area shown at left” or “See detail of Portland area at right.” Another is using a colored rectangle on the main map that matches the border of the inset, so your eye naturally links the two. Interestingly, professional cartographers generally avoid “zoom lines” (those converging lines that make it look like the inset is magnifying out of the main map). While they seem intuitive, they tend to add visual clutter without improving clarity.
Each inset map should have its own scale bar if it’s at a different scale than the main map. Since the whole point of an inset is usually to show something at a different zoom level, a single scale bar for the entire layout would be misleading. In mapping software like ArcGIS, scale bars are tied to individual map frames, so when you add an inset at a different scale, you associate a separate scale bar with it.
Inset Maps in Digital Tools
In modern geographic information systems (GIS), creating inset maps is a standard layout feature. Software like ArcGIS lets you place multiple map frames in a single layout, each with its own geographic extent, scale, and associated elements like scale bars and legends. You can set one frame as your main map and add others as insets, positioning and sizing them independently.
Digital mapping has also extended the inset concept into interactive applications. Esri’s Insets template, for example, displays noncontiguous locations within a single app layout so users can view and interact with data from multiple areas simultaneously. You can customize which geographic areas appear as insets, adjust their size, and reorder them. This is particularly useful for organizations that need to present data across scattered locations, like a company tracking operations in several disconnected regions, without forcing users to pan back and forth across a single map.
The core idea, though, hasn’t changed since paper maps: an inset map is simply a second (or third) map view embedded alongside a primary one, giving you context or detail that the main map can’t provide at its own scale.