Documentation

## Annotate a Web Map with Measurement Information

This example shows how to use a map to get information about a geographic feature. To illustrate, this example measures the length of the Gross Reservoir and adds some markers and a line overlay that act as annotations on the map.

Open a web map centered on the Gross Reservoir west of Boulder, Colorado. Use the USGS Shaded Topographic Map to get the level of topographical detail required for this measurement.

```webmap('usgsshadedtopographicmap') lat = 39.94823; lon = -105.3637; zoom = 14; wmcenter(lat, lon, zoom) ``` Identify two points at opposite ends of the lake and get the latitude and longitude of these points. To get this information in a web map, move the mouse pointer over a location on the map. In the upper right corner, the Web Browser displays the geographic coordinates of the point. The following figure shows how to find latitude and longitude information of a point in a map using the web map browser. Store the latitude and longitude information in a geoshape vector.

```lat1 = 39.93515; lon1 = -105.38034; lat2 = 39.95226; lon2 = -105.35892; s = geoshape([lat1, lat2],[lon1 lon2]) ```
```s = 1x1 geoshape vector with properties: Collection properties: Geometry: 'line' Metadata: [1x1 struct] Vertex properties: Latitude: [39.9524 39.9359] Longitude: [-105.3588 -105.3803]```

Calculate the distance between the two points to get the length of the reservoir. Use the `distance` function which calculates the distance between points on a sphere or ellipsoid.

```d = distance(s.Latitude(1),s.Longitude(1),s.Latitude(2), ... s.Longitude(2),wgs84Ellipsoid)```
```d = 2.6383e+03```

Draw a line between the two points. Include information about the length of the lake in the line’s information balloon. Store the distance and information about units as two dynamic fields added to the geoshape vector.

```s.Distance = round(d); s.Units = 'meters'; wmline(s, 'Color', 'red', 'FeatureName', 'Length of Gross Reservoir', ... 'Overlayname', 'Transect'); ```  