Key Takeaways
- A mapping review is a transparent, systematic form of evidence synthesis that identifies, describes, and catalogs the research available on a broad topic; it answers the question “what do we know about this area?”
- Unlike a systematic review, a mapping review does not synthesize study results or appraise study quality; it classifies studies against predefined codes and presents them in tables, graphs, or interactive maps.
- Mapping reviews belong to the “Big Picture” review family, alongside scoping reviews and evidence and gap maps (EGMs), and they are especially useful for identifying research gaps and setting research priorities.
- A registered, a priori protocol, a PRISMA flow diagram, and a predefined coding framework are the 3 pillars of a rigorous mapping review.
Contents
- Glossary of Key Terms
- What Is a Mapping Review?
- Mapping Review Example
- Systematic Review vs Mapping Review
- Scoping Review vs Mapping Review
- Mapping Review Protocol
- Tips for Undergraduate and 1st-Year PhD Students
- Frequently Asked Questions
- Sources and Further Reading
Glossary of Key Terms
| Term | Definition |
| Mapping review | A systematic approach to identifying, describing, and cataloging the evidence and evidence gaps on a broad topic, using predefined codes and descriptive data extraction. |
| Evidence synthesis | The rigorous collation, evaluation, and analysis of studies, reports, and other literature to inform decision making. |
| Scoping review | An exploratory evidence synthesis that maps the breadth of evidence on a topic, clarifies concepts, and may code data inductively or deductively. |
| Systematic review | An evidence synthesis that answers a focused question, appraises study quality, and synthesizes results, often with meta-analysis. |
| Evidence and gap map (EGM) | A visual, often interactive, matrix that plots available studies against a predefined framework of interventions and outcomes to reveal gaps. |
| Coding framework | The predefined set of categories (for example, population, intervention, study design, country) against which each included study is classified. |
| A priori protocol | A written plan, prepared and ideally registered before the review begins, that specifies the question, criteria, and methods. |
| PRISMA flow diagram | A standard chart that reports how many records were identified, screened, excluded, and included in a review. |
| Grey literature | Research produced outside commercial publishing, such as dissertations, reports, working papers, and conference proceedings. |
| Critical appraisal | Formal assessment of the quality or risk of bias of included studies; typically omitted in mapping reviews. |
What Is a Mapping Review?
A mapping review is a transparent, rigorous, and systematic method for identifying, describing, and cataloging the available evidence, and the evidence gaps, in a broad topic area. It answers questions such as “what do we know about this topic?” or “what research exists, and where?” It describes the research landscape rather than pooling study findings.
Mapping reviews typically extract only descriptive, high-level information about studies and apply predefined codes to classify them. The output is usually visual: tables, charts, bubble plots, heat maps, or an interactive evidence and gap map. Because the goal is description, not synthesis, results of individual studies are usually not combined or summarized in depth.
The term “evidence mapping” was first used by Katz and colleagues in 2003 and has roots in the natural sciences. The approach was later developed by groups such as the EPPI-Centre, the Collaboration for Environmental Evidence, the Campbell Collaboration, and the International Initiative for Impact Evaluation (3ie). Mapping reviews rarely appeared in the literature before 2009 but have grown rapidly since.
How Does a Mapping Review Work?
A mapping review works by running a systematic search, screening records against explicit inclusion criteria, coding each included study against a predefined framework, and then plotting the coded studies in tables or graphics. The typical stages are summarized below.
| Stage | What Happens |
| 1. Question and protocol | Define a broad but answerable question; write and register an a priori protocol with a coding framework. |
| 2. Search | Run systematic, documented, repeatable searches across databases and grey literature; scope may be limited to certain study or publication types. |
| 3. Screening | Apply inclusion and exclusion criteria, ideally with 2 independent reviewers; record numbers in a PRISMA flow diagram. |
| 4. Coding and extraction | Extract descriptive data (population, setting, design, intervention, outcomes measured) and apply the predefined codes. |
| 5. Mapping and reporting | Present frequencies and distributions in tables, charts, or an EGM; describe clusters of evidence and gaps. |
When Should You Use a Mapping Review?
Use a mapping review when the literature is large and diverse, when you need a big-picture overview before committing to a focused systematic review, or when your goal is to identify research gaps and inform research priorities. It suits closed, descriptive questions such as “how often is this term used, and in which populations?”
Common purposes include:
- Charting what types of evidence exist in a field and where research is concentrated.
- Identifying gaps to guide future primary research, funding calls, or commissioned reviews.
- Informing policy audiences that need an overview of a broad area rather than an answer to 1 narrow question.
- Serving as a first step toward building the “evidence architecture,” for example, locating existing reviews and clusters of primary studies that could support guidelines.
Strengths and Limitations of Mapping Reviews
Strengths:
- Handles very broad questions with multiple interventions, outcomes, and study designs.
- Offers a uniquely transparent, rigorous method for identifying research gaps.
- Produces accessible visual outputs that help policymakers and funders locate evidence quickly.
Limitations:
- No synthesis of findings and usually no quality appraisal, so it cannot tell you whether an intervention works.
- Broad scope means high screening workloads, and pragmatic search limits may miss some studies.
- Conduct and terminology remain inconsistent across disciplines, and visual outputs may require extra skills or software.
Mapping Review Example
A frequently cited example is the 2019 mapping review of gambling harm research by Baxter, Hilbrecht, and Wheaton, published in Harm Reduction Journal. The authors mapped research on gambling harm across 3 regulatory environments to show where evidence was concentrated and where it was missing.
| Element | How the Example Handled It |
| Question | What research exists on gambling harm in 3 different regulatory environments? |
| Search | Systematic, documented searches across multiple databases, covering a defined time period. |
| Screening | Explicit inclusion and exclusion criteria applied to a large volume of records. |
| Coding | Studies classified with predefined codes such as topic, population, jurisdiction, and study type. |
| Output | Tables and charts showing the distribution of studies, plus a narrative description of evidence clusters and gaps. |
| Use | Findings used to highlight under-researched harms and populations, informing future research priorities. |
Other well-known applications include Campbell Collaboration evidence and gap maps on transport interventions, disability, and employment and health in low- and middle-income countries. A country evaluation map was even used by the Office of the Prime Minister of Uganda to locate studies for policy work.
See also: Literature Mapping in Research: Definition, Types, and Benefits
Systematic Review vs Mapping Review
A systematic review answers a narrow, focused question, most often about the effectiveness of a specific intervention. A mapping review addresses a much broader territory and stops at describing and cataloging the evidence. The 2 designs share systematic searching and screening but diverge sharply after that point.
| Feature | Systematic Review | Mapping Review |
| Question | Narrow and focused, for example, does drug X reduce mortality? | Broad and descriptive, for example, what research exists on condition Y? |
| Scope | 1 intervention or exposure, defined outcomes | Multiple interventions, outcomes, designs, and contexts |
| Quality appraisal | Required; risk of bias assessed for each study | Usually none; appraisal only if clearly justified |
| Synthesis | Full synthesis of results, often meta-analysis | No synthesis of results; description and classification only |
| Output | Pooled effect estimates, conclusions, recommendations | Tables, charts, maps of the evidence base and its gaps |
| Typical use | Clinical or policy decisions on effectiveness | Research prioritization, gap identification, review planning |
Timeframes are similar: a well-conducted mapping review can take 12 months or more, about as long as a systematic review, because the broader scope generates many more records to screen even though data extraction per study is lighter.
Scoping Review vs Mapping Review
Scoping reviews and mapping reviews are close relatives, and the literature often uses the terms interchangeably. Methodologists such as Campbell, Khalil, Tricco, and colleagues argue that a useful distinction exists: the 2 designs sit on a spectrum within the same “Big Picture” family but differ in question type, coding approach, and depth of extraction.
| Feature | Scoping Review | Mapping Review |
| Question type | More open and exploratory, for example, how is a concept defined in the literature? | More closed and descriptive, for example, how often is the concept studied, and in which groups? |
| Coding | Inductive or deductive; categories can emerge from the literature | Deductive; codes are predefined in the protocol |
| Depth of extraction | Deeper, more textual and descriptive data per study | Lighter, high-level descriptive data across more studies |
| Breadth | Often narrower topic, fewer studies, richer analysis | Often broader topic, more studies, thinner analysis |
| Typical output | Narrative plus tables; concept clarification | Tables, graphs, and frequently an accompanying EGM |
| Guidance | JBI methodology and the PRISMA-ScR reporting checklist | Draws on scoping review guidance; dedicated guidance still developing |
The historical roots also differ. Scoping reviews grew from the sociological framework of Arksey and O’Malley (2005), later advanced by Levac and colleagues. Evidence mapping emerged from the natural sciences via Katz and colleagues (2003), and was adopted by environmental science and international development organizations.
In practice, a single project can combine both: a review may “scope” concepts and “map” study characteristics. What matters is stating clearly which approach you followed, using consistent terminology, and reporting your methods transparently so readers can judge the rigor of the work.
Mapping Review Protocol
An a priori protocol is strongly recommended for every mapping review. Writing the protocol before searching protects the review from bias, because the coding framework, the very “map” against which evidence is plotted, is fixed in advance rather than shaped by the results the team hopes to find.
What Goes Into a Mapping Review Protocol?
A mapping review protocol specifies the review question, objectives, eligibility criteria, search strategy, screening procedures, the predefined coding framework, and the planned visual outputs. The table below lists the core components.
| Component | What to Include |
| Title and team | Working title identifying the design as a mapping review; team members, roles, and any stakeholder or information specialist involvement. |
| Background | Why the map is needed; existing reviews on the topic; the decision or research agenda the map will inform. |
| Question and objectives | A broad but closed question, structured with a framework such as PO (population, outcome) or PICO elements where relevant. |
| Eligibility criteria | Inclusion and exclusion criteria for population, concept, context, study designs, publication types, dates, and languages. |
| Search strategy | Databases, grey literature sources, search strings, and any pragmatic limits, written to be repeatable. |
| Screening plan | Number of reviewers, pilot screening, conflict resolution, and the commitment to a PRISMA flow diagram. |
| Coding framework | The predefined codes and categories for data extraction, drawn from an accepted typology or built with stakeholders. |
| Analysis and outputs | Planned tables, graphs, or interactive EGM; how frequencies, clusters, and gaps will be described. |
| Registration and dissemination | Where the protocol will be registered or published, and how the map will be shared and updated. |
Register or publish the protocol where possible. Options include the Open Science Framework, Figshare, protocols journals, and organization-specific routes such as Campbell Systematic Reviews for evidence and gap maps. PROSPERO currently focuses on reviews with health-related outcomes and does not accept scoping or mapping reviews, so plan an alternative venue early.
For reporting the completed review, many teams adapt the PRISMA 2020 statement and the PRISMA-ScR extension for scoping reviews, since dedicated mapping review reporting guidance is still maturing. State explicitly which checklist you followed and how you adapted it.
Tips for Undergraduate and 1st-Year PhD Students
A mapping review is one of the most realistic evidence synthesis projects for an early-career researcher, but the breadth that makes it attractive can also sink it. The tips below will help you finish on time and produce something publishable.
- Confirm the design fits your question: if your supervisor expects conclusions about effectiveness, you need a systematic review; if you want to chart what exists, a mapping review is right. Use a review-selection tool, or the comparison tables above, before committing.
- Talk to a librarian in week 1; an information specialist will save you months by refining search strings, recommending databases, and helping you estimate the size of the literature before you commit.
- Pilot everything: test your search on 1 database, screen 50-100 records, and trial your coding framework on 10 studies before scaling up; revise the protocol while revision is still cheap.
- Keep the coding framework short; 8-12 well-chosen codes beat 30 ambitious ones, because every extra code multiplies extraction time across hundreds of studies.
- Use reference management and screening software from day 1, and document every decision; your PRISMA numbers must add up when you write the report.
- Recruit a 2nd screener, even for 20% of records; dual screening with conflict resolution is a marker of rigor that reviewers and examiners look for.
- Budget 12 months or more, and agree on scope limits (dates, languages, publication types) with your supervisor in writing to prevent scope creep.
- Plan the visuals early; sketch the tables, bubble plots, or EGM matrix you want to produce, then make sure your coding framework captures exactly those variables.
- Frame the gaps carefully; identify them from the map itself, not from your own research agenda, and be transparent if the review paves the way for your thesis.
Frequently Asked Questions
What is the difference between a mapping review and a literature review?
A traditional literature review is narrative and unsystematic; the author selects sources at their discretion. A mapping review follows a registered protocol, systematic searches, explicit criteria, and predefined codes, and it reports its methods so another team could reproduce the map.
How long does a mapping review take to complete?
Plan for 12 months or more. Although data extraction per study is light, broad questions can return thousands of records to screen, so the total effort is similar to, or greater than, a standard systematic review. If time is a concern, a focused rapid review may be a better choice.
Does a mapping review include critical appraisal or risk of bias assessment?
Usually not. Because a mapping review describes rather than synthesizes evidence, quality appraisal is optional and often omitted. If you include it, justify the choice and report the tool used.
What is the difference between a mapping review and an evidence and gap map?
An EGM is a visual, often interactive, matrix that plots studies against a predefined framework of rows and columns. A mapping review may include an EGM as its output, but it can also stand alone with tables and graphs; an EGM can likewise be published independently.
Can a mapping review be published as a standalone paper?
Yes. Mapping reviews are published in methods, disciplinary, and evidence synthesis journals, and organizations such as the Campbell Collaboration publish full mapping reviews and EGMs. A clear protocol, PRISMA flow diagram, and transparent coding greatly improve acceptance odds.
What reporting guidelines should I use for a mapping review?
Dedicated mapping review guidance is still developing, so most teams adapt PRISMA 2020 or the PRISMA-ScR checklist for scoping reviews, and follow JBI methodological guidance where applicable. Always state which checklist you used and describe any adaptations.
How many studies do you need for a mapping review?
There is no minimum or maximum. The number depends on the breadth of the question and the eligibility criteria; published maps range from under 100 to several thousand included studies. What matters is that the search is systematic and the map represents the field fairly.
Is a mapping review the same as a systematic map?
Essentially, yes. “Systematic map” is the preferred term in environmental sciences, following the Collaboration for Environmental Evidence, while health and social sciences more often say “mapping review” or “evidence map.” The core method, systematic searching plus descriptive coding, is the same.
Sources and Further Reading
- Campbell F, Tricco AC, Munn Z, et al. Mapping reviews, scoping reviews, and evidence and gap maps (EGMs): the same but different, the “Big Picture” review family. Systematic Reviews. 2023;12:45.
- Khalil H, Tricco AC. Differentiating between mapping reviews and scoping reviews in the evidence synthesis ecosystem. Journal of Clinical Epidemiology. 2022;149:175-182.
- University of South Florida Libraries. Systematic Reviews for Social Sciences: Mapping Review. LibGuide, updated 2026.
- Sutton A, Clowes M, Preston L, Booth A. Meeting the review family: exploring review types and associated information retrieval requirements. Health Information and Libraries Journal. 2019;36(3):202-222.
- James KL, Randall NP, Haddaway NR. A methodology for systematic mapping in environmental sciences. Environmental Evidence. 2016;5:7.
- Campbell F, Sutton A, Pollock D, et al. Guidance on the conduct and reporting of mapping reviews in Research Synthesis Methods and related methodological literature.
- Baxter DG, Hilbrecht M, Wheaton CT. A mapping review of research on gambling harm in three regulatory environments. Harm Reduction Journal. 2019;16:12.
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