# Prepare geo data (with basemap)

## Introduction

In order to create a [mapchart](/visualizations-and-layouts/creating-visualizations/viz-gallery/legacy-viz-designs/mapchart.md), the dataset used to create the chart must include a geographical column that give information about the polygon corresponding to a zone. So within this page, we will see more in detail the pre-requisite in term of data preparation that will allow the creation of a mapchart.

{% hint style="info" %}
When building a mapchart, the geographical column will be **automatically used** in order to build the chart. There is no need to specify it, but it's **mandatory** to have this geographical column.
{% endhint %}

Generally, for a mapchart building purpose, you will need:

* 1 **basemap** file (**geojson** format): file contaning the geographical polygon of a label (for example regions, countries, ...)
* 1 datasource / dataset containing your measure and dimension
* Depending on the need in term of data preparation, there are some **YouPrep** **steps** that are dedicated for geographical data.

The overall process is simple:

* Import the basemap file (it should have the extension **geojson**)
* Create a dataset containing your measure and dimension
  * Join the basemap dataset
* (Make some data transformation)
* Create a mapchart using the dataset containing your measure, dimensions, and geographical column

## Example of a complete process

* Import the basemap file in Toucan.

Generally the file will contains a list of geographical label (e.g Country, Region, ...) with associated geographical polygons (column geometry in the example below).

<figure><img src="/files/VFDKi5R4OqZs38VbxM1N" alt="" width="563"><figcaption></figcaption></figure>

* Create a new dataset containing all the measures & dimensions, and JOIN the basemap dataset to your dataset with YouPrep. In the example below, we join the dataset containing geographical column (`basemap_france`) to our dataset, by using the key `Departement`

  <figure><img src="/files/1j2hdLqQxEExKxBU0kjd" alt="" width="563"><figcaption></figcaption></figure>
* After having join the basemap dataset, you should see new column coming from the joined dataset, and most importantly you should find your column contaning the geographical data (`geometry` in the example) that has the **correct column type (geo)**.

  <figure><img src="/files/hms5VlutYhyyYG6bAmYC" alt="" width="563"><figcaption></figcaption></figure>
* You can also make some data transformation that are specific to geographical data

  <figure><img src="/files/Hb27JU5uLwGRE3iFwHW0" alt="" width="563"><figcaption></figcaption></figure>
* Then, save the dataset.

{% hint style="success" %}
The dataset is now ready to be used in order to create a mapchart.
{% endhint %}

So, you can now easily create a mapchart (look at the [mapchart documentation](/visualizations-and-layouts/creating-visualizations/viz-gallery/legacy-viz-designs/mapchart.md) more detail) using the dataset you just created.

<figure><img src="/files/ZFOhEcmIIYfGu0aR6iGb" alt=""><figcaption></figcaption></figure>


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