There are 6 categories of field data intel to be collected comprising of a total of 293 collectible items.
Collecting all items in each category will unlock a specific item of clothing and of course an achievement / trophy.
The intel items are found as you move through the city and appear on your map once you have passed in close proximity to them. So making a full exploration of the city will help you find all of these. Your menu pages will show you which items you have found and the locations so you will have an idea of where else to search.
A further help is available for these. When activating and upgrading the Tech wing of the Base of Operations choosing to activate the Canine Unit you will unlock the perk 'intel Discovery'. With this perk when you complete all of the Side Missions and Encounters in a zone of the city then all the intel items in that zone will appear on your map.
The Survival Guidebook intel are pages from the book "New York Collapse: An Urban Catastrophe Survival Guide" by Warren Merchant.
Phone Recordings are phones that are found around Manhattan with messages left on the phone. They give insight to what was happening in people's lives a few weeks before and into the catastrophe.
There are ten incident reports to be found for each enemy faction in the game.
Crashed Drones have information on them that gives the agents intelligence on the current state of Manhattan.
If you are having trouble locating one... look up. They can be found dangling from parachutes on buildings. Shoot the drone to bring the intel pickup down.
Missing Agents intel gives information on the first wave of Division Agents that entered the city before your activation and have not been heard from for a long time.
The Evidence Correlation Holographic Overlay system, or ECHO for short, reconstructs a 3D image with some information on the people there at the time. This gives agents clues as to what has been happening in New York recently.
Many of the Echos are found as part of Side Missions so will not need to be searched for.