---
title: "Define a z-mod area"
slug: "how-to-define-a-z-mod-area"
description: "Learn to modify topographic elevation by defining a zmod area"
tags: ["topographic features", "shapefile", "building models", "2D modelling"]
updated: 2023-06-21T14:08:56Z
published: 2023-06-21T14:08:56Z
canonical: "help.floodmodeller.com/how-to-define-a-z-mod-area"
stale: true
---

> ## Documentation Index
> Fetch the complete documentation index at: https://help.floodmodeller.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Define a z-mod area

Modifying the elevation of an area within your model can be used for specifying elevations for proposed defences, filling holes/areas of missing data in your underlying DTM, and much more.

To create a z-mod feature, you must initially define the location for the modification. This can be an area (i.e. polygon), a line, or a single point within your 2D domain.

![](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/definezmodarea(1).PNG?sv=2026-02-06&spr=https&st=2026-11-14T11%3A46%3A18Z&se=2026-11-14T12%3A46%3A18Z&sr=c&sp=r&sig=1ls7Bu7nCtn%2BiM6RZAxZDyWvHIeIughoOdUSUq7pPyY%3D)

Note:

If you already have an area defined within a shapefile, you can load this into Flood Modeller and then proceed to [use the z-mod vertices tool](/v1/docs/how-to-use-the-z-mod-vertices-tool).

### Steps

1. On the **2D Build** tab, within the **Z mod** section, click **Z polygon**, **Z line** or **Z points**, as appropriate. Select a suitable name and save location for the shapefile.
2. In the **Layer Editor** tab, click **Polygon**, **Line** or **Point**, as appropriate, and draw your polygon in the usual fashion. Don't forget to click **Save** and then **Stop Edit** when you have completed your shape.
3. You will now need to proceed to [use the z-mod vertices tool](/v1/docs/how-to-use-the-z-mod-vertices-tool) to fill the vertices with the new elevation data required.