How to make a source map

Which people, documents and personal observations bear witness to these events?

When searching for sources it is not only about who and what, but also about where and when. Where are the people and documents located? And when, in the course of events, do they come into view? That is why we not only make a list of potential sources, but also place them on a “map”.

As with the hypothesis and the timeline, the same applies here: use your imagination. Focus on the sources you want to obtain before you start searching and interviewing.

Ask yourself for each individual event in your story:

Which stakeholders and witnesses can I interview about the event? Who is likely to be willing to speak with me?
Which public documents (publications), such as websites, articles, reports and books, can shed light on the subject?
Which confidential or private documents might I be able to obtain?
What can I observe, experience or test myself? Which relevant locations can I visit? Which objects can I describe or handle myself?

You can present the answers in a table, as in this example:

TIMELINE	INTERVIEWS	PUBLICATIONS	OBSERVATIONS
Pipe manufacturers choose the cheapest chemicals.	• Supplier
• Manager of pipe factory	• Price comparison
Chemical manufacturers sell the harmful chemicals to pipe manufacturers.	• Manager of chemical factory
• Spokesperson of chemical factory		• Purchase order
Inspectors check drinking water for chemicals other than the harmful ones.	• Inspector
• Legal regulations
• Inspection report		• On the road with an inspector
Pipe manufacturers produce plastic water pipes with harmful chemicals.	• Manager or process operator	• Patent
• Recipe
• Tour of factory
Plumbers install more water pipes of plastic than other materials.	• Plumber
• Annual report
• Database
• Articles in trade journals		• On the road with a plumber
Chemical scientists see chemicals from plastic water pipes migrating into drinking water.	• Erik Arvin	• Scientific article in Water research, 36 (2002)	• Visit to laboratory
Doctors report deaths due to the harmful chemicals.	• Health Care Inspectorate
• Doctor	• Database
• Report
Cell biologists see chemicals deforming human cells in their labs.	• Cell biologist
• Scientific article		• Visit to laboratory
Scientists send an urgent letter to the EC calling for a ban on these chemicals.	• Initiator
• MEP	• Urgent letter

The purpose of a source map is to think of as many sources as possible before you actually begin your investigation. Again, use your imagination. Brainstorm. An ideal source map contains sufficient reliable sources, in the different categories, to be able to start the investigation. The map shows whom you can interview, but also which documents you should request in the interviews and where you can meet. You do not have to consult all of these sources, but it is good to know what options exist. Some sources are more attractive or more reliable than others. And not everyone will want to talk to you, and not all documents will be shared. The source map helps you not only to brainstorm possible sources, but also to make considered choices, such as:

Which source is the richest; contains the most (reliable) information?
Which is the most powerful, the most persuasive?
Which is the most surprising or richest in emotion (dramatic)?
Which is the most vivid?
Which documents are the most difficult to obtain?
Which source can you use if your first choice turns out to be unavailable?