diff --git a/api/src/Map.js b/api/src/Map.js
index d5754d0e4ab7..c4089a6c8175 100644
--- a/api/src/Map.js
+++ b/api/src/Map.js
@@ -42,6 +42,17 @@ import * as themes from './Themes.js';
  * @property {string} [icon]
  */
 
+/**
+ * @typedef {Object} MapOptions
+ * @property {string} div
+ * @property {import("ol/coordinate.js").Coordinate} center
+ * @property {number} [zoom=10]
+ * @property {boolean} [showCoords=true]
+ * @property {boolean} [addMiniMap=false]
+ * @property {boolean} [miniMapExpanded=true]
+ * @property {boolean} [addLayerSwitcher=false]
+ * @property {Array<string>} [layers]
+ */
 
 /**
  * @private
@@ -50,17 +61,9 @@ import * as themes from './Themes.js';
 class Map {
 
   /**
-   * @param {Object} options API options.
-   * @property {string} div
-   * @property {import("ol/coordinate.js").Coordinate} center
-   * @property {number} [zoom=10]
-   * @property {boolean} [showCoords=true]
-   * TODO: more options
+   * @param {MapOptions} options API options.
    */
   constructor(options) {
-    if (!constants.extent) {
-      throw new Error('Missing extent');
-    }
     /**
      * @private
      * @type {View}
@@ -74,7 +77,7 @@ class Map {
 
     if (options.center !== undefined) {
       this.view_.setCenter(options.center);
-    } else if (constants.extent !== undefined) {
+    } else if (constants.extent) {
       this.view_.setCenter(getCenter(constants.extent));
     }
 
diff --git a/api/src/constants.js b/api/src/constants.js
index 04ccac60a33c..3972095bc425 100644
--- a/api/src/constants.js
+++ b/api/src/constants.js
@@ -6,18 +6,26 @@ import EPSG21781 from '@geoblocks/proj/src/EPSG_21781.js';
  * @property {?string} themesUrl
  * @property {string} projection
  * @property {Array<number>} resolutions
- * @property {?[number, number, number, number]} extent
+ * @property {[number, number, number, number]} [extent]
  * @property {string} backgroundLayer
  */
 
-export default /** @type {APIConfig} */({
+export default {
+  // The URL to the themes service.
   themesUrl: null,
+
+  // The projection of the map
   projection: EPSG21781,
+
+  // The resolutions list.
   resolutions: [250, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.25, 0.1, 0.05],
-  extent: null,
-  /**
-   * The name of the layer to use as background. May be a single value
-   * (WMTS) or a comma-separated list of layer names (WMS).
-   */
+
+  // The extent restriction, must be in the same projection as `config.projection`.
+  // the format is `[minx, miny, maxx, maxy]`for example: `[420000, 30000, 660000, 350000]`
+  // the default is ǹo restriction.
+  // extent: undefined,
+
+  // The name of the GeoMapFish layer to use as background. May be a single value
+  // (WMTS) or a comma-separated list of layer names (WMS).
   backgroundLayer: 'orthophoto',
-});
+};