<esri:FeatureLayer.MapTip>
     <Grid>
      <Grid.ColumnDefinitions>
       <ColumnDefinition Width="Auto"/>
       <ColumnDefinition Width="*"/>
      </Grid.ColumnDefinitions>
      <ItemsControl ItemsSource="{Binding Keys}" Grid.Column="0" />
      <ItemsControl ItemsSource="{Binding Values}" Grid.Column="1" />
     </Grid>
    </esri:FeatureLayer.MapTip>