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Find research gaps automatically through reference gaps

Most review papers forget to cite key references. These reference gaps are the easiest way to spot research gaps in a field you are not familiar with. We will use one of the most sophisticated but simple literature search tools to uncover reference gaps and discover new research gaps.

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Since you are looking for a research gap, I assume you are already somewhat familiar with your field. If not, find some key review papers and read them to get a feel for the main keywords. You will need popular review papers for this workflow. To become familiar with a field use a visual strategy to learn it quickly and efficiently.

The process is easy but somewhat unconventional, so let’s break it down:

  1. Find starter papers 1-5 (too many will not be beneficial). These should ideally be review papers, as they have the most citations and should cover an entire field without leaving gaps.
  2. Use LitMaps to pull out all references (yes, these are 100s of papers) into a single map
  3. Adjust the graphical layout to “Map Relevance” to see the gaps better. (This is the magic of Litmaps and the reason why I am such a huge fan of this tool)
  4. Run a search for similar papers. As we already have a collection of 100s papers, this will give only a few results, but they will be the gaps we seek.
  5. Analyze the resulting papers in more detail to uncover the research gap.

1. Finding a review paper

The key to finding citation and research gaps is to start with the right papers. The best way to start is with a recent review paper. A review paper’s goal is to cover an entire field. That means that whatever is left out of a review is a possible gap. A review paper will usually have many more citations than other papers.

I found a paper titled “Improvements in reports of species redistribution under climate change are required” for this example. It is an extensive review of my subject.

2. Upload your paper to Litmaps

Next, go to and create a Litmap to add just this one paper to it. A Litmap is a graphical representation of a set of papers. Connections on this map are references or citations. Initially, the layout is determined by the recency and citation count of the papers. When adding a first paper, Litmaps will display a number of related papers as white circles. They are irrelevant at the moment; don’t let them confuse you.

3. Add the paper’s references

Click on the paper you uploaded (Taheri 2021 in my example). This will bring up a small dialogue on the side containing the abstract, title, and a few other things. Find the button titled “References” and click on it. Here, you can see all 286 references. We need to select them and add them to the Litmap.

If you have more papers, repeat this process for each paper. In my experience, having more than 300-400 papers in total on a Litmap will overwhelm the UI.

4. Switching to “Map Relevance” view

The legend is at the bottom left of your Litmap. Clicking on it allows you to customise how the papers are laid out on the map. By default, the horizontal axis is recency; papers on the left are older, and papers on the right are newer. Select “Map Relevance” as your vertical axis, replacing the citation count.

This layout pushes the most connected papers in your litmap to the top. Naturally, our original paper (Taheri 2021) will be at the very top, as it is connected to all the papers below. But there will be a few papers in the mid-range. These are the central papers of your domain. If you don’t know them, read them. They are at the top because everybody cites and knows them; you should, too!

5. Discover the reference gap

Finally, click the “Explore Related Articles” button. Litmaps will now search for papers not part of this litmap but are tightly linked/related. They will be displayed as white circles. It is worth unpacking why this is important. We started with a review paper and its references. It should contain the most relevant papers for the field. Any papers linked to this large set will likely be on the same topic and thus relevant. However, if these papers are not part of the original review paper references, they are reference gaps that the original authors did not mention.

At the top left of your litmap you can switch the view from “ring” to standard. This arranges the papers by map relevance. Notice how “Lenoir 2020” (white circle, right center) is a very prominent reference gap in Taheri 2021. In this case Lenoir 2020 might have been published after Taheri 2021 was submitted (it can take years from submission to publication) and thus it is a recent development rather than a research gap. But there are many more papers Litmaps will find that are less recent (white circles in the video).

6. Dig deeper into gap papers

Now that Litmaps has found research gaps for you, there is one more hack you can do. Click on the Lenoir 2020 paper (our reference gap) and see the “Overview” button in the left sidebar. Litmaps will bring up a few related papers. If the documents are displayed as a grey circle, they are already part of the bitmap and irrelevant. You can select the white circles (they aren’t part of your litmap yet) and add them to the litmap. This will direct the Litmaps search towards papers mentioned in your reference gap paper. Update the results to get new and refined suggestions.

During the entire process, save papers that jump at you because they seem relevant and save them for later reading.

7. Tag the “Gap Papers” and collect them

Next, we will collect all the “gap papers”, i.e. Litmaps’ suggestions that are not part of our collection yet. Remember, all of these papers are highly relevant to the subject of the first paper but, for some reason, were not mentioned in it. We need to find out why this is to identify a research gap. Tag all the papers that match the topic. Not all of Litmap’s suggestions will be good suggestions; use your best judgment.

Note that Litmaps displays 10 suggestions at a time. Scroll to the bottom of the list on the left and click on the right arrow to load the next 10. They will replace the previous ten on the litmap. You can keep digging like this as long as you like but the relevance of the suggested papers will generally drop after 20-30 papers.

8. Analyse the citation gap collection

After collecting a few of these research gap papers, you need to look at them and see if you notice any similarities. Click on the tag at the top left to reveal all the papers. Clicking on them will bring out the abstract, and these papers will be displayed in orange on the litmap, allowing you to see how they connect.

We are trying to figure out what unites all these gap papers. In ecology I might ask:

  • Are these gap studies done in plants rather than animals?
  • Maybe they deal with the southern vs the northern hemisphere?
  • Maybe they are modeling approaches rather than observational studies

You will have found the research gap if you have found the uniting characteristic! For example, suppose all the gap studies deal with data collected in the southern hemisphere. In that case, we have a research gap that can be formulated as “Little is known about the climate change impacts on plants and animals of the southern hemisphere, as most studies are conducted in the northern hemisphere”. This can then become a paper that specifically looks at this issue.

9. Final Remarks

This method finds reference gaps, papers that an author could have cited but didn’t. Sometimes, this may be because the authors were unaware of the publication, which is an actual research gap. For example, in ecology, climate change-related papers can be published on animals or plants; reviews on plants often don’t mention animals and vice versa. This method will reveal this lack of synthesis! Then, for example, you can start thinking about a research question relating to the similarities of plant and animal responses to climate change and might find novel insights. This is how this method can help you in tracking the research gap.

Moreover, this method works great for your unpublished work. If you are writing a literature review, use this method to double-check if you have covered everything you need by uploading the references directly to Litmaps. This process is part of the Effortless Literature Review and involves extracting your references as a bib file and uploading it to Litmaps.


In this tutorial we used LitMaps to find references an author of a review paper might have forgotten. These are possible research gaps linking closely related fields together and allowing you to ask novel research questions.

  1. Start with 1-5 key review papers.
  2. Add them and their references to a large litmap with up to 400 papers.
  3. Configure your litmap to show “Map relevance” on the vertical axis to spot the most common papers.
  4. Ask Litmaps to find new related papers for this collection. These are the “gap papers”.
  5. Analyse them further by exploring the “Litmaps Overview”.
  6. Collect all “gap papers” and find similarities between them
  7. Identifying similarities might lead you to find a research gap

This method will be part of the upcoming webinar on research gaps:

Identifying research gaps is the most important first step in contributing impactful science. Join this webinar to learn how to find the critical gaps in your own field using a clear, step-by-step strategy. I’ll share a three-part process that includes effective note-taking, visualizing knowledge, and finding research gaps. All with practical, easy-to-follow examples for you to apply to your own research.