Hello,

Welcome back to the mini-series on the basic elements of an index! I previously discussed entries and arrays, main headings and subheadings, and locators. Today I am writing about cross-references.

Cross-references are a type of locator, but instead of directing readers to the text, cross-references redirect readers to a location within the index. Riffing off the metaphor of an index as a map, I like to think of cross-references as signposts within the index that ensure readers find the arrays they want.

Cross-references come in two types, See and See also. See references tell the reader, “Good effort, but the information you want is actually over there,” while See also references indicate, “if you liked this, maybe you will also like that.”
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How to Use

• Cross-references should always point to new information, which is to say, new locators that the reader hasn’t seen yet. If the array the cross-reference is pointing towards has identical locators, then it is a double-post, which is also good, but renders a cross-reference unnecessary.
• Speaking of double-posts, cross-references and double-posts are kind of like cousins, complementary tools for making information accessible within the index. Double-posts are when identical information is placed in two or more locations in the index, such as both a main heading and subheading, to accommodate readers searching either way. They work best for shorter strings of locators that are easily duplicated. The downside to double-posts is that they can take up space, especially if subheadings are involved. In that case, a cross-reference is the quicker and more space efficient option.
• Cross-references are usually from broader topics to more specific topics. For example, “computers. See also Apple; Microsoft.” The logic is that readers less clear on what they are looking for will likely begin with the broader term, whereas if they already have the specific in mind, they will skip the broader term and go straight to the specific. For those readers uncertain, the cross-reference prompts them that there is more to the topic that they may be interested in. Can cross-references also go in the opposite direction, from specific to broad? Yes, sometimes. I don’t want to create a hard-and-fast rule, but I usually find broad-to-specific to be more meaningful. Think carefully about which direction readers are likely to desire.
• Building upon broad-to-specific, cross-references can also be used if a subheading needs to be hived off to create its own array. Say “Apple” is originally a subheading under “computers,” but as the index is created it accumulates a dozen locators, which you decide should be broken down into subheadings. Instead of using sub-subheadings under “computers,” turn “Apple” into its own array and use a cross-reference to redirect readers.
• Cross-references can also be reciprocal. Say the book contains two or more related, but not quite identical, concepts. Cross-references are a good way to link these arrays, keeping in mind that readers should find something new in each.
• Cross-references can link synonymous terms. Say the book uses the terms “film industry” and “movie industry,” and you decide to make “film industry” the preferred term in the index. A cross-reference should be used to redirect readers who search for “movie industry.” A cross-reference from “Hollywood” may also be a good idea, if the book is specifically about the American film industry.
• Cross-references can also be generic. There may be a category of arrays that you want to point readers towards and there are too many to list. For example, in a work of US history that covers multiple presidencies, the following may be useful: “United States of America. See also specific presidents.” The assumption here is that readers will know the names of specific presidents, or will remember which are discussed in the book, and will be able to search accordingly.

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Formatting and Placement

Where to place the cross-reference is an interesting question. The cross-reference is usually placed at the end of the array, after the other locators and subheadings, if any. But cross-references can also be placed at the beginning, immediately after the main heading.

For example,

and

Both approaches have their advantages. Placing cross-references at the end allows the reader to first peruse the array to see if they can find what they want. If not, the cross-references are ready to offer other suggestions. Placing cross-references at the beginning allows readers to quickly see if they actually want to be elsewhere, before they dig into the subheadings. Placing cross-references at the end is more common, and I think is what most readers and publishers expect. However, for reference documents, especially, and for indexes with very long arrays, placing the cross-references at the beginning can be helpful for an audience that wants to search quickly.

Cross-references can also direct readers to specific subheadings. I rarely do this, but that may have to do with the types of books I tend to index. If you need to, the cross-reference can be phrased as either “statistics. See also under economics” or “statistics. See also economics—statistics.”

Cross-references can also be attached to specific subheadings, instead of being gathered in a group at the beginning or end of the array. I didn’t use to do this, but the recent NISO indexing standard (ANSI/NISO Z39.4-2021) recommends doing so, which prompted me to give this more thought and to adjust my practice. There are two questions that guide where I place the cross-reference: 1) How specific is the cross-reference? Is it more connected to the main heading or to the subheading? 2) How long is the array? If short, I think readers will easily see the cross-references at the end. If long, then attaching the cross-reference to the subheading, if relevant, allows the reader to be redirected sooner.

In terms of formatting, See and See also are typically upper case and in italics. The exception is if the heading being directed to is also in italics. For example, “Austen, Jane. See Northanger Abbey; Persuasion; Pride and Prejudice.” Multiple cross-references are separated by semicolons. Cross-references are preceded by a period, but, if placed at the end of an array, no closing punctuation is needed. Cross-references attached to subheadings are in lower case and may be placed in parentheses to better differentiate from the surrounding subheadings. For example, “literature: authorship, 34, 53, 122; figurative language, 45, 53 (see also metaphor; similes); poetry, 56-60, 132, 154; translation (see translation)“

Some indexes are thick with cross-references, an interlocking web redirecting readers. This may be due to the book using a lot of synonyms, or similar but different terms, or concepts for which the indexable term is not obvious. Other indexes contain just a handful of cross-references. Either way, the goal is to ensure that readers find the information they desire.

I have two more posts coming up in this mini-series on the basic elements of an index, on formatting and sorting. I'm looking forward to it.

Happy indexing,

Stephen