How to Map Your System Landscape in One Afternoon – The C1.5 Shortcut

You’ve just stepped into a new role – maybe as CTO, maybe as Head of Development – and as usual, the architecture is a maze or even completely missing. Documentation is outdated, knowledge is scattered, and no one holds the full picture. Without a map, you’re flying blind.

You could spend weeks reading thru confluence, readme and code, piecing things together, but there’s a shortcut:

In this post, I’ll show you how to map a “good-enough” system landscape in one afternoon using a lightweight, practical shortcut of the C4 framework I call C1.5.

Why Mapping Matters

If you don’t have a map of the system, you’re flying blind.

• Misaligned priorities
  Teams optimize locally, but nobody’s optimizing globally.
• Blind spots
  Hidden dependencies lurk until they break in production.
• Firefighting mode
  You’re reacting instead of leading.

On the flip side, even a rough system map creates instant leverage:

• Alignment
  Engineering, product, and leadership can finally point at the same picture.
• Decision-making
  You can weigh trade-offs with more confidence.
• Leadership presence
  A simple diagram signals clarity and control.

C1.5 – A Practical Shortcut

The C4 Model for software architecture describes four levels of diagrams from System Context to Code.

On day one, you don’t need full container diagrams, let alone components or code. What you do need is:

1. a System Landscape showing all major systems, who owns them, and how they connect (slightly broader than a single C1 diagram), and
2. a few lightweight Context sketches for the most critical systems.

That’s somewhere between C1 and C2 – not as detailed as containers, but more than just one context. I jokingly call this C1.5: the sweet spot for gaining clarity fast.

Here’s the simple, four-step process I use to map it:

Step 1: Sketch the Landscape

Start broad. Put all the company’s systems and external dependencies on paper.

• Rule of thumb: each team = one system.
• If a team has none → add a “?” placeholder.
• If a team has multiple → mark it and dig deeper later.

This gives you an immediate sense of ownership, coverage, and gaps.

Step 2: Refine with Key Players

Grab time with product, ops, and development leads. Show them the landscape and update it live as they talk.

• Ask about critical systems, pain points, and dependencies.
• Cross-check assumptions across different perspectives.
• Add the people or teams you talk to as actors, and connect them to systems.

You won’t get to everyone in an afternoon, but even a few voices will sharpen the picture.

Step 3: Trace the Critical Paths

With PMs/POs, zoom into their most important user journeys.

• Draft System Context diagrams just for these critical paths.
• Show the actors, the system in question, and its immediate neighbors.
• Ignore edge cases – focus on what delivers value day to day.

This ties the technical landscape directly to business outcomes.

Step 4: Capture Relations

As you go, capture the different ways people and systems connect. Examples I often use:

Relation	Meaning	Example
Owns	Accountable for the system	Payments squad owns the Payment Service
Builds	Develops or extends it	Backend team builds the Order Service
Operates	Runs or supports it	Ops team operates the Monitoring stack
Uses	Interacts with it	Sales uses the CRM
Calls	One service calling another’s API	Order Service calls the Payment API

You don’t need every relation on day one. Just map what’s known, possible, and useful. Different orgs emphasize different relations – adapt to the processes you find.

Choosing the Right Tools

Tools matter, but don’t overcomplicate it. On day one, the best choice is always the tool you already know — you won’t master a new diagramming framework in an afternoon. Whether that’s a whiteboard, Miro, PowerPoint, or Structurizr, stick to what you can use fluently and without friction.

Equally important is accessibility. The map has little value if it’s hidden behind licenses or niche skills. Everyone in the company should be able to open it, comment on it, and understand it at a glance.

Once the initial map has buy-in and becomes part of the team’s workflow, that’s the right time to consider moving it into a proper C4 model with something like Structurizr or PlantUML. Models scale, enforce consistency, and let you generate multiple diagrams from a single source of truth — but only after the organization is ready to use and maintain them.

👉 Rule of thumb: speed and accessibility first, structured models later.

I have personally used PlantUML with C4-PlantUML, Structurizr and Draw.io (on Confluence). Depending on the company, existing tools, current documentation & assets, as well as team and architecture maturity, they address different pain-points and provide different strengths. However, evaluation of the perfect architecture modelling tool for your organization isn’t simple and takes a lot of knowledge, time and effort.

What About EA Teams and Tools?

Depending on the scale and maturity of the organization, you may already find people or even whole teams doing parts of this work. Larger companies often have enterprise architects, application catalogs, or service registries.

That’s valuable, and it can be a great input to your own map. But don’t confuse it with what you need on day one.

EA catalogs are often exhaustive, governance-driven, and hard to digest. Your first priority is clarity: a lightweight system landscape that reflects how people actually work with the systems today. The act of sketching and refining the map together is as important as the artifact itself.

So yes – many CTOs have people and tools for that and much more. If you do, use them. But still go through the exercise yourself, because it builds shared understanding, exposes gaps, and earns trust fast.

Final Thoughts

As a new leader, the first map you draw is first and foremost for yourself. You need to understand the landscape well enough to make decisions, see dependencies, and ask the right questions.

The map doesn’t need to be perfect — it needs to be useful. By sketching a lightweight “C1.5” view, you create a common picture that others can validate, challenge, and refine. That shared understanding quickly becomes more valuable than the diagram itself: it helps teams align, exposes blind spots, and connects product priorities to technical reality.

Speed helps, but the real point is clarity. And clarity is what lets you lead with confidence from day one.