# Mapping tools – Geometries - Isochrones

The " Mapping Tools " feature allows you to:

- draw geometries, free contours, circles, polygons and isochrones on the map,
- draw and search for Locations, Sites, Projects, Retailers present or absent in all types of geometries (see next chapter “ To know the commercial offer present in a Geometry or Isochrone ")
- draw and measure,,
- perform spatial operations, union, difference and intersection of geometries.

## Geometry – Definition

“A Geometry is a set of geometric data describing the shape and position of geographical data. The geometric data are represented by points, lines or surface areas and identified in the selected system, thus superimposable with the other data. All geometries occupy a position in space, defined by their interiors, boundaries and exteriors. The exterior of a geometry is the whole space not occupied by the geometry. The interior is the space occupied by the geometry. The boundary of a geometry is the location between its interior and its exterior.”

## Draw

Under the " Draw " section, you will find the different geometries that will allow you, through notes and symbols on the map, to make personalised annotations thanks to which you will be able to highlight the points you want and communicate your analysis in a clear and professional way. A range of tools is at your disposal: arrows, lines, surface areas, circles, text boxes of varying size and colour.

Arrow : Click on the map to define the origin of the arrow. Move the cursor to define its length and direction. Click to define the target of the arrow.

Line : Click on the map to define segments. Double-click to finish.

Custom text : Enter the text in the fields below and place it on the map using the “Place on the map” button.

Circle : Click on the map to define the centre of the circle. Move the cursor to define its diameter. Click to finish. Set the opacity to 0% so that the inside of the geometry is transparent.

Contour : Click on the map to define the vertices. Double-click to finish. Set the opacity to 0% so that the inside of the geometry is transparent.

Freehand contour : Draw freehand on the map by holding down the left mouse button. Set the opacity to 0% so that the inside of the geometry is transparent.

## Draw an isochrone

The “Isochrone” feature allows you to display one (or more) isochrone(s) on the map

“An isochrone is a curve that connects the accessible points in a given travel time, from a starting point and using a chosen means of transportation.”

Calculate and display an "Isochrone" on the map, i.e. calculate and display the curve that links up the points accessible in a given travel time from a starting point using a selected mode of transport.

Example: On the map, draw the isochrones that can be accessed by car in 10, 20 and 30 minutes from the Place d’Armes in Namur (BE).

- Click on "Select a point" and click on the map to position the starting point. Then, define the travel time, the mode of transport and the colour.
- Clicking on "Draw the isochrone" launches the calculation and the isochrone will be displayed on the map.
- Select new parameters for the other isochrones.

For your own information: Codata Explorer uses the service "Graphhopper Isochrone" to get these curves and to display them on the cartographic interface. This service calculates the travel time based on OpenStreetMap’s road network and on free-flowing traffic conditions.

Precise information about the used data and algorithm are available on this page of the website https://www.graphhopper.com.

## Draw and measure

The “Draw and measure” section offers you two tools to measure distances, perimeters and surface areas.

For a distance, click on "Length" and select the starting point with a left click. Define the distance from a selected marker and conclude with a double left click. The distance is displayed in the center of the plotted geometry.

For a surface area, click on “Surface area” and select the vertices of the surface area you wish to measure with a left click and conclude with a double left click. The surface area is displayed in the centre of the geometry.

## To perform a spatial operation

The “Spatial operations” mapping tool allows you to represent and highlight an intersection, addition or difference of two polygons, whether they are geometries, Isochrones or any type of polygon.

In order to illustrate this tool and to show the differences between an intersection, an union and a difference of two polygons, we will take the example of a circle and a contour represented on the Urban Unit of Lyon and which each encompass several sites.

After drawing the two polygons on the map, click on the first polygon and then on the second one (a green "v" surrounded by a circle appears next to the polygons selected in the right menu). Then choose the type of spatial operation (Intersection, Union, Difference), the color and the opacity percentage of the geometry that will represent the intersection between the two polygons (in the following examples, red and 50%). Then click on "Draw the result".

### Intersection

### Union

### Difference

## Load a geometry

You can save any drawn geometry (see next chapter “ To know the commercial offer present in a Geometry or Isochrone ") and then reload it from the cartographic interface or the “Location(s)/Site(s)” criterion of the search engines.