old_contents: import React, { PropTypes } from 'react';
  import slug from 'slug';
  
  export default class MapPOILegend extends React.Component {
  
  	constructor (props) {
  		super(props);
  	}
  
  	render () {
  		let pois = [
  			{ 
  				icon: 'icon_bench',
  				iconSize: [30, 20],
  				label: 'benches'
  			},
  			{ 
  				icon: 'icon_picnic-table',
  				iconSize: [30, 20],
  				label: 'picnic tables'
  			},
  			{ 
  				icon: 'icon_boat-launch',
  				iconSize: [30, 20],
  				label: 'boat launch - existing'
  			},
  			{ 
  				icon: 'icon_boat-launch',
  				iconSize: [30, 20],
  				label: 'boat launch - planned'
  			}
  		];
  
  		return (
  			<div className='map-poi-legend'>
  				{ pois.map(poi =>
  					<div>
  						<svg
  							key={ poi.label }
  							width={ poi.iconSize[0] }
  							height={ poi.iconSize[1] }
  							className={ slug(poi.label) }
  						>
  							<use xlinkHref={ '#' + poi.icon } />
  						</svg>
  						<div className='label'>{ poi.label }</div>
  					</div>
  				)}
  			</div>
  		);
  	}
  
  }
  
new_contents: import React, { PropTypes } from 'react';
  import slug from 'slug';
  
  export default class MapPOILegend extends React.Component {
  
  	constructor (props) {
  		super(props);
  	}
  
  	render () {
  		let pois = [
  			{ 
  				icon: 'icon_bench',
  				iconSize: [30, 20],
  				label: 'benches'
  			},
  			{ 
  				icon: 'icon_picnic-table',
  				iconSize: [30, 20],
  				label: 'picnic tables'
  			},
  			{ 
  				icon: 'icon_boat-launch',
  				iconSize: [30, 20],
  				label: 'boat launch - existing'
  			},
  			{ 
  				icon: 'icon_boat-launch',
  				iconSize: [30, 20],
  				label: 'boat launch - planned'
  			}
  		];
  
  		return (
  			<div className='map-poi-legend'>
  				{ pois.map(poi =>
  					<div key={ poi.label }>
  						<svg
  							width={ poi.iconSize[0] }
  							height={ poi.iconSize[1] }
  							className={ slug(poi.label) }
  						>
  							<use xlinkHref={ '#' + poi.icon } />
  						</svg>
  						<div className='label'>{ poi.label }</div>
  					</div>
  				)}
  			</div>
  		);
  	}
  
  }
  
subject: Put the `key` on the right element, to shut up React.