Ask A Cartographer

Inset Map

February 14 2008 | 2 comments
Categories: Cartographic Design

Are there cartographic standards for inset location maps? I am locating a study region within a larger area on an inset map. What elements are generally included on inset maps? I have attached a map, in a first draft, to show my first attempts.

Mapping Center Answer:

First, consider the purpose of the inset map. Inset maps are sometime used to show related themes of data on maps at a smaller scale. More often, inset maps can be used to either provide an overview of the area or provide a close up of a section or sections of the map. If the inset map is used to provide an overview, consider your audience and determine what locational information they need to properly fix the location of your study area in their minds. When the inset map is used to provide a close up view of a portion of the map, you area able to provide further detail in areas that are rather congested on the main map. Sometimes close ups of areas are also used of the area shown on the inset if that area is of particular importance to the message you are conveying.

Second, inset maps will either be open or closed forms. A closed form is one that has an outline that the map readers will immediately recognize (the U.S., Italy, the world, a state, etc.) An open form is a section of any of these that will be a little harder for the reader to place locationally without additional information, unless your audience is already familiar with how you have cropped the area shown in the inset. 

If you are using a closed form, familiarity will already allow you to get away with providing less base locational information for the audience. If you using an open form, you may need to give the audience more clues about the area. Base data generally includes some or all of the following: administrative boundaries, hydrography, major transportation, cultural features (e.g., cities), physiography (if it makes sense for the mapped area and theme). 

There are a few standards that you can follow. In general, the same design considerations that you apply to the main map should be applied to the inset map(s). Here are some tips:

  • When you use an inset, be sure to make a clear distinction between the inset and the main map (a border, drop shadow, etc. can help). To provide the reader with clues as to the relationship between the inset and the main map, you can either use captions like "Area shown at left", or "See detail of Portland area at right". If you have multiple insets, you can label them 1, 2, 3, or A, B, C or you can label them with their location ("NE corner", "Western half", etc.) and use the same label as the title of the inset maps.
  • It is not usually helpful to use "zoom lines" (lines that make the map look like it zooming out from the map) – map readers are familiar enough with inset maps that this addition to the page is not really necessary.
  • Sometimes all that is required to show the area that you are mapping on an overview map is very simple base data with a few geographic details (e.g., a state with the county outlines). Then the area shown on the man map is simply a polygon that is filled in with a solid color or an outline around the area shown on the main map. If you use a border for the main map, a clever trick is to use the same color (usually black) as the border for the polygon fill or outline on the overview map.
  • If the scale of the overview map is global, you do not need to provide a scale indicator (i.e., graticule, representative fraction, scale bar, etc.) If you are showing any other scale, you would want to use a scale indicator.
  • If you are showing any orientation other than "North is Up", include an orientation indicator (i.e., north arrow or graticule) for the inset map.
  • • Make sure that the level of generalization is appropriate for the scale of the inset map – if you are showing an overview of your study area, the data in your inset should be more generalized. Take a look at MapShaper if you need help making your features less detailed (this is an online tool that allows you to input shapefiles, generalize the linework, get it back out, and use it on your own maps).
  • The substantive design (that is, the "look and feel") of the inset map should be the same as the "look and feel" of your main map – use similar colors, fonts (albeit usually smaller ones), etc.
  • • Use the locator map to balance the content on the page – often inset maps can be used as "anchoring" elements, this is because they have straight edges, so placing them along the bottom of the map can help to “anchor” the content of the page making the page seem more "grounded".
  • Relate the content of the inset map to the theme of the page, not just the main map – usually insets are used to help tell a story or provide additional vantage windows into the theme. 

You can find additional information about these and other map elements in:

  • Brewer, Cynthia A. 2005. Designing Better Maps. Redlands, CA: ESRI Press, 202 pages, ISBN-10: 1589480899, ISBN-13: 978-1589480896.

  • Robinson, Arthur H., Joel L. Morrison, Phillip C. Muehrcke, A. Jon Kimerling and Stephen C. Guptill. 1995. Elements of Cartography, Fifth Edition. New York, NY: John Wiley & Sons, Inc., 674 pages, ISBN 0-471-55579-7.

  • Slocum, Terry, Robert B. McMaster, Fritz C. Kessler, and Hugh H. Howard. 2005. Thematic Cartography and Geographic Visualization, Second Edition. Upper Saddle River, NJ: Pearson Prentice Hall, 518 pages, ISBN 0-13-035123-7.

confusing language posted by Chris McGirr on Jun 9 2009 11:40AM
This needs clarification as the roles of inset and overview maps are sometimes reversed. Examples would be useful, and the second paragraph is unclear. Possibly, it uses the word "closed" where it should be "open". Additionally there are several mispellings and bad edits.
Thanks -- we did this already! posted by Aileen Buckley on Jun 9 2009 1:08PM
Actually, I did clean up the content and add graphics to the blog entry that I wrote as a follow up to this Ask a Cartographer question. Take a look at "Cartographic Design: Inset Maps" (http://blogs.esri.com/Support/blogs/mappingcenter/archive/2008/03/04/cartographic-design-inset-maps.aspx) and hopefully it will help you more. If not, we look forward to additional comments!

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