Inset Map or Locator Map: Which One Your Figure Needs

Reference
Study Area Map MakerLocator panels, extent boxes and connector lines that stay attached when you move a panel.Open the Study Area Map Maker

The words get used loosely. People call any small map inside a bigger one an inset, and then argue about whether it should zoom in or out. Both versions exist, they answer different questions, and a figure often needs both.

Three side by side illustrations. The first shows a main map with a small corner map that zooms out to a country outline with a red box, labelled locator inset. The second shows a main map with a red box on it and a corner map that zooms in on that box to reveal three overlapping sites, labelled detail inset. The third shows two equal panels joined by dashed connector lines. A footer states the rule for choosing between them.
The corner map in the first two panels looks identical in a layout. It is doing the opposite job in each.

Locator inset: zooms out

A small map in a corner showing a wider area, with a box marking where the main map sits. It answers one question: where on earth is this.

You need one whenever a reader outside your region cannot place your study area. In practice that is nearly always, because journals are read internationally and a district name means nothing to somebody two continents away. The locator carries almost no detail: an outline, a highlight, a box. No scale bar, no grid, no labels beyond a country name if it helps.

Detail inset: zooms in

A small map showing a magnified piece of the main map, usually a crowded corner where several sites sit on top of each other. It answers a different question: what is inside that cluster.

You need one when the scale that suits the study area as a whole is too coarse for part of it. Six boreholes within two kilometres of each other in a study area two hundred kilometres across will overlap into a single blob, and no amount of symbol shrinking fixes that. Draw a box on the main map, magnify it, and connect the two with lines so the reader can see where the magnified piece came from.

Side by side panels: when neither fits in a corner

Sometimes the corner map has nowhere to go. Every corner of your main map has data in it, or the locator needs to be big enough to be legible, or you have three scales to walk down rather than two. Then the small map stops being an inset and becomes a panel of its own, joined to the main panel by connector lines.

This is what the two panel and cascade layouts do. It costs more page width and it never covers your data, which is why it has become the default in most earth science journals.

How to choose

Two questions.

Can a reader point to your study area on a map of the country? If not, you need a locator, in a corner or as its own panel.

Do any of your sites overlap at the scale the rest of the map needs? If so, you need a detail inset. Note that this is about the scale the map needs, not the scale you would prefer. Zooming the whole map in to separate two sites usually pushes the rest of the study area off the frame.

Needing both is completely normal, and a figure with a locator panel on the left, a main map in the centre and a magnified detail in a corner is a standard and perfectly readable arrangement.

Rules that apply to both

The box has to be findable. A box two millimetres across on the printed page is a smudge. If your study area is genuinely that small relative to the locator, use an arrow or a filled marker instead of an outline, or move the locator to a tighter extent such as the province rather than the country.

The frame has to be obvious. A thin grey rectangle around a corner map disappears against a pale background. A solid dark frame, or a small drop of white space around it, tells the reader that this is a separate map and not part of the main one.

The connector lines, when you use them, must actually connect the box corners to the panel corners. Hand drawn connectors that no longer line up after somebody nudged a panel are one of the more common reasons a figure gets sent back, and they are why it is worth letting a tool compute them.

Neither small map needs its own scale bar. The locator does not have a meaningful one, and the detail inset can state its own bar if the magnification is large, but a bar on a two centimetre corner map is usually clutter.

What to call it in the caption

Be specific rather than correct. Nobody will object to inset shows the location of the study area within Kenya, and everybody understands it. What causes confusion is a caption that says only inset, leaving the reader to work out which direction it went. One clause solves it.

The study area map maker builds the locator pattern directly: the box on any panel is the extent of the next panel, and the connector lines are computed from where the panels actually sit, so they stay attached when you move things.

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