--- title: "Horizontal vs Vertical Discovery In ServiceNow: What Each Tells You" description: Horizontal discovery finds your infrastructure. Top-down discovery shows which services depend on it. Here's when each fits, and what a gap costs. image: https://www.apexconfiguration.com/hubfs/AI-Generated%20Media/Images/Engineer%20With%20Tablet%20In%20Data%20Centre%20Aisle.png --- [![APEX CONFIGURATION GROUP](https://www.apexconfiguration.com/hs-fs/hubfs/Act3%20child/images/ACG-logo.png?width=135&height=93&name=ACG-logo.png "APEX CONFIGURATION GROUP")](https://www.apexconfiguration.com/) [![APEX CONFIGURATION GROUP](https://www.apexconfiguration.com/hs-fs/hubfs/Act3%20child/images/ACG-logo.png?width=135&height=93&name=ACG-logo.png "APEX CONFIGURATION GROUP")](https://www.apexconfiguration.com/) - [Home](https://www.apexconfiguration.com) - ServiceNow - [ServiceNow CMDB](https://www.apexconfiguration.com/servicenow-cmdb) - [CMDB Health Check](https://www.apexconfiguration.com/cmdb-health-check) - [CMDB Design & Implementation](https://www.apexconfiguration.com/cmdb-design-implementation) - [Managed Service](https://www.apexconfiguration.com/managed-cmdb-services) - [Automation & Optimisation](https://www.apexconfiguration.com/cmdb-automation-tools) - Maximising ServiceNow - [CMDB Health Dashboard](https://www.apexconfiguration.com/cmdb-health-dashboard-servicenow) - [CMDB Dependency Mapping](https://www.apexconfiguration.com/cmdb-relationship-table) - [CMDB Configuration Items](https://www.apexconfiguration.com/cmdb-configuration-items) - [CMDB Workspace](https://www.apexconfiguration.com/cmdb-workspace-servicenow) - [CMDB Best Practice](https://www.apexconfiguration.com/cmdb-best-practices) - [ServiceNow Discovery](https://www.apexconfiguration.com/servicenow-discovery-setup) - [Service Mapping](https://www.apexconfiguration.com/servicenow-service-mapping) - About - [How We Help](https://www.apexconfiguration.com/about-apex) - [What is a CMDB?](https://www.apexconfiguration.com/what-is-cmdb) - [Benefits](https://www.apexconfiguration.com/benefits-of-cmdb) - Resources - [Blog](https://www.apexconfiguration.com/blog) - [Contact Us](https://www.apexconfiguration.com/contact-us) [Contact Us](https://www.apexconfiguration.com/contact-us) [Contact Us](https://www.apexconfiguration.com/contact-us) - [Home](https://www.apexconfiguration.com) - ServiceNow - [ServiceNow CMDB](https://www.apexconfiguration.com/servicenow-cmdb) - [CMDB Health Check](https://www.apexconfiguration.com/cmdb-health-check) - [CMDB Design & Implementation](https://www.apexconfiguration.com/cmdb-design-implementation) - [Managed Service](https://www.apexconfiguration.com/managed-cmdb-services) - [Automation & Optimisation](https://www.apexconfiguration.com/cmdb-automation-tools) - Maximising ServiceNow - [CMDB Health Dashboard](https://www.apexconfiguration.com/cmdb-health-dashboard-servicenow) - [CMDB Dependency Mapping](https://www.apexconfiguration.com/cmdb-relationship-table) - [CMDB Configuration Items](https://www.apexconfiguration.com/cmdb-configuration-items) - [CMDB Workspace](https://www.apexconfiguration.com/cmdb-workspace-servicenow) - [CMDB Best Practice](https://www.apexconfiguration.com/cmdb-best-practices) - [ServiceNow Discovery](https://www.apexconfiguration.com/servicenow-discovery-setup) - [Service Mapping](https://www.apexconfiguration.com/servicenow-service-mapping) - About - [How We Help](https://www.apexconfiguration.com/about-apex) - [What is a CMDB?](https://www.apexconfiguration.com/what-is-cmdb) - [Benefits](https://www.apexconfiguration.com/benefits-of-cmdb) - Resources - [Blog](https://www.apexconfiguration.com/blog) - [Contact Us](https://www.apexconfiguration.com/contact-us) [Contact Us](https://www.apexconfiguration.com/contact-us) [tel:+442080588135](tel:+442080588135)[mailto:contact@apexconfiguration.com](mailto:contact@apexconfiguration.com) [Service Mapping](https://www.apexconfiguration.com/blog/tag/service-mapping)[ServiceNow](https://www.apexconfiguration.com/blog/tag/servicenow) [ITOM](https://www.apexconfiguration.com/blog/tag/itom)[ServiceNow Discovery](https://www.apexconfiguration.com/blog/tag/servicenow-discovery) # Horizontal vs Vertical Discovery In ServiceNow: What Each Tells You [![Warren O'Neill](https://www.apexconfiguration.com/hs-fs/hubfs/warren-oneill.webp?width=40&height=40&name=warren-oneill.webp)](https://www.apexconfiguration.com/blog/author/warren-oneill) by [Warren O'Neill](https://www.apexconfiguration.com/blog/author/warren-oneill) 5 min read Oct 23, 2026, 9:00:02 AM Last updated on 23 Oct 2026, 09:00:02 Horizontal discovery in ServiceNow scans across your estate and records every device it can reach, with its direct relationships. Vertical, or top-down, discovery starts from a business service's entry point and follows its connections down to the infrastructure that service depends on. Horizontal discovery answers "what do we have?". Top-down discovery answers "what breaks if this goes down?". Change and incident management need both answers, and the gap between them is where shared infrastructure goes unnoticed until a change takes several services offline. ## Key Takeaways - Horizontal discovery scans across your estate and records every device it can reach, with its direct relationships. It answers "what do we have?". - Top-down discovery, delivered through service mapping, starts from a service entry point and follows connections down to the infrastructure the service depends on. It answers "what breaks if this goes down?". - Top-down discovery needs horizontal discovery underneath it, because it uses the same credentials and discovery servers and draws its maps over configuration items that already exist. - Tag-based mapping is only as accurate as the people doing the tagging. At one broadcaster it showed a shared component supporting one application, and a change took several applications offline at a cost of $600,000 in advertising revenue. - Decide what to map top-down first by business criticality and by shared infrastructure with the most incoming relationships, and have each service owner confirm the entry point. - Make impacted services a mandatory output of change risk assessment, and consult every service owner where a configuration item supports more than one service. ## What horizontal discovery gives you Horizontal discovery works range by range. It classifies each device, identifies it against the configuration management database (CMDB), and explores its hardware, software, processes and immediate connections. The result is a broad infrastructure layer: servers, network devices, storage, databases, and the installed software on each. Relationships are local, such as a database running on a server or a server connected to a switch. What it can't tell you is purpose. A server with a web server process and a database connection is a server. Discovery can't know that it carries the payroll run, or that three other applications also depend on it. ## What top-down discovery adds Top-down discovery, delivered through service mapping, starts from an entry point you define, such as a web address, a load balancer or a message queue. It uses patterns to identify the application at that entry point, then follows its outbound connections to the next component, and the next. The output is an application service: a map of the specific CIs that deliver one service, in the order traffic flows through them. Change impact, incident impact and business criticality all depend on those maps. Top-down discovery needs horizontal discovery underneath it. The map is drawn over CIs that already exist, using the same credentials and discovery servers. | | Horizontal discovery | Top-down discovery | | --- | --- | --- | | Starts from | Network ranges | A service entry point | | Produces | Infrastructure CIs and local relationships | Application services and their dependency chain | | Answers | What exists, and where | What a service depends on | | Needs from you | Ranges, credentials, schedules | Entry points, service owners, working horizontal discovery | ## Where tag-based and manual mapping fall short Service mapping also supports tag-based mapping, which groups CIs into a service using tag values applied in the source platform or by hand. It's quick to stand up, and it's only as accurate as the people doing the tagging. On one broadcaster's estate, application managers were asked to tag the components that supported their applications. Much of the underlying infrastructure served several applications at once. Each manager tagged components only with the application they considered most important. A change was then raised against a critical piece of infrastructure. The service maps showed it supporting one application. When it was taken offline, several business applications and services failed, including the advertising schedule application. Commercial breaks went out with no commercials. The loss in advertising revenue came to $600,000. A later application audit found that the applications that failed had no service map at all. Problem management linked the incidents to the change after the event. We replaced the tag-based maps with top-down, pattern-based service mapping, which records every service a shared component supports, whatever anyone considers its main one. ## Deciding what to map top-down first Mapping every application at once stalls. Choose an order the change advisory board can defend. **Rank by business criticality.** Start with the services whose failure has a direct revenue, safety or regulatory cost. **Find the shared infrastructure.** Report on infrastructure CIs with the highest number of incoming relationships from horizontal discovery. Those are the components where a single change can hit several services. The services running on them go early in the queue. **Confirm each entry point with its owner.** A map built from the wrong entry point is precise and wrong. The service owner signs off the entry point and reviews the first map. **Check horizontal coverage first.** If the ranges and credentials underneath a service aren't working, top-down discovery will stop partway and return a partial map. ## Keeping both layers useful to change and incident A map that isn't used in change assessment stays a diagram. Make impacted services a mandatory output of change risk assessment for any CI that appears in a map. Where a CI supports more than one service, require every service owner to be consulted, and record them in the RACI (responsible, accountable, consulted, informed) for that service. Track two key performance indicators (KPIs): the proportion of business-critical services with a current top-down map, and the number of incidents where problem management had to establish impact after the event. The second number should fall as the first rises. Review each map on a schedule, and whenever a major change touches its components. Our article on [service mapping and the CMDB data model](https://www.apexconfiguration.com/blog/cmdb-data-model-security-ai-performance) covers the wider effect of mapping on security and incident work. ## How Apex helps Our discovery and integration coverage review establishes what is missing from your estate view, where, and what it costs during an incident. It covers both layers: which ranges horizontal discovery reaches, and which critical services lack a trustworthy top-down map. We scope it with you at an initial consultation. If you need a starting position for the change advisory board, our two-week CMDB health baseline scores which configuration items (CIs) are trustworthy and which are guesses. [Book a CMDB diagnostic call](https://www.apexconfiguration.com/cmdb-diagnostic-call) or [arrange a meeting with a consultant](https://www.apexconfiguration.com/book-a-meeting). ## Frequently asked questions ### Can we do top-down discovery without horizontal discovery? Not reliably. Top-down mapping uses the same discovery servers and credentials, and it depends on infrastructure CIs being identified cleanly. Without horizontal discovery, maps stop partway or create duplicates. ### Is tag-based mapping ever the right choice? It can suit environments where tags are applied automatically by the platform and enforced, such as some cloud estates. Where tags depend on people, expect gaps on shared components. ### How do we find infrastructure shared by several services? Count incoming relationships per infrastructure CI, and compare the result with the services that CI appears in. A heavily connected CI in only one map is worth checking first. ### Who should own a service map? The service owner owns what the map should contain. 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