Legend Types

There are three legend types. They determine not only how important layers are displayed in Touchstone, but also how those layers are analyzed. The availability of the legend type options depends on the type of data stored in the field that you select in the Analysis Field. When you pick a text or alphanumeric field, you can only select the Single Symbol or Discrete Values legend type. If you select a numeric field, you can choose any of the three legend types.

•       Single Symbol: Displays all objects (for example, points, lines, and polygons) in the map layer using the same "symbol”. This legend type is used to display objects uniformly in the layer, such as red fill for all states or blue border for all state boundary lines. When you select Single Symbol, Touchstone treats all the objects in the layer as a single type of category when used for accumulations or for hazard intersections. If you select Single Symbol, users will not be able to apply different damage ratios while configuring accumulations. This legend type is useful for data that shows binary information such as storm surge potential or no storm surge potential, flooded or not flooded, etc.

•       Discrete Values: Displays categorical data using unique symbols. A unique symbol is assigned to each category. Features with matching category values are drawn using an assigned symbol. Touchstone not only displays the various categories using the Legend Type, but also analyzes the same categories for accumulation or for hazard intersections. For example, the shapefile that you are importing may have many polygons with a field showing high, medium and low flood depths. In this example, the discrete values will display in the same colors chosen for these values. While configuring an analysis, users can apply different damage ratios for each of the three categories. Similarly, if the user is configuring hazard intersections, the results will automatically show how much value is concentrated in each of these three categories.

•       Banded Ranges: Defines the ranges when displaying quantitative data for a given numeric field, data which is typically counts, amounts, or ratios. For example, you can map data representing wind speed, precipitation, radioactive contamination, and population quantitatively. The Minimum and Maximum values that bracket each range determine which feature falls into each range and how the ranges appear on the map. In Touchstone, the minimum value of the range is inclusive, and the maximum value of the range is exclusive. For example, in the European Windspeed footprint layer legend, all values up to 65 are included in the range of 0-65, while value 65 is included in the 65-88 range.

•       The Units option for Banded Ranges enables you to specify the measurement units to appear on the legend. You can type in your own measurement, select from the list (Feet, Kilometers, Meters, Miles, and Mixed Values), or leave this field blank for unit-less data. For example, if your data contains Ground Acceleration values, you could enter m/s (meters per second) in the box. You must specify the units before creating the legend colors, etc. Otherwise, when you change the unit’s value, Touchstone scans the file again and all the legend information is gone.

•       The Banding option enables you use one of two predefined methods for segmenting ranged data into groups for visualization. The Equal Distribution setting divides the range of attribute values into equal-sized sub-ranges based on the defined number of ranges. The Natural Breaks setting creates a legend that attempts to minimize deviation within each band (as set by the  number of bands). For large datasets, the Natural Breaks method may take significantly longer to compute than the Equal Distribution method. If you want to define your own classes, you can manually add the number of bands and then set class ranges that are appropriate for your data. Alternatively, you can start with one of the standard classifications and make adjustments as needed.

•       The Number of Bands option enables you to specify the number of bands you want to apply to the data. When you select this option, editable rows appear in the bottom portion of the window.

At this time, Touchstone does not support any continuous data types. For example, if you have a raster dataset that shows the depth of flooding at every pixel, you must import the data using banded ranges.