# Visibility Data Layers

**URL:** <https://community.purpleair.com/t/visibility-data-layers/154>\
**Category:** Data Layers\
**Created:** [October 27, 2021, 7:37pm UTC](https://community.purpleair.com/t/visibility-data-layers/154 "2021-10-27T19:37:05Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![PurpleAir](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/purpleair/32/176_2.png) [@PurpleAir](https://community.purpleair.com/u/PurpleAir)\
**Post date:** [October 27, 2021, 7:37pm UTC](https://community.purpleair.com/t/visibility-data-layers/154/1 "2021-10-27T19:37:05Z")

</div>

The “Data Layer“ field determines which indices, scales, or metadata to display on the _Map Markers_, graphs, and the map legend. The default field-selection is “US EPA PM2.5 AQI“.

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## Visibility Layers

This next partition of data layers is a section of visibility indices. Data for the indices are supplied by the laser counters within the PurpleAir sensors. Choose a data layer from the following section to present the sensor data within the standard index.

[**Fine particulate light scattering (Mm -1)**](https://map.purpleair.com/1/mSC/): This field selection portrays the attenuation of light due to scattering by particles as it passes through a medium. In the case of visibility, attenuation or extinction refers to the loss of image-forming light as it passes from an object to the observer. See, [Visibility Basics](http://vista.cira.colostate.edu/Improve/visibility-basics/) by Colorado State University.

The light scattering, for a wavelength of 550 nm, in inverse megameters ( \text{Mm}^{-1} ), due to fine particulate is given by:

b\_\text{sb1} = 0.015 n

where the particle count per deciliter of particles greater than 0.3 \mu \text m is n.

[**Deciviews (dv)**](https://map.purpleair.com/1/mDV%7C1.2/): This field selection displays unit of measurement of haze, or “haze index”. Deciview is a measure of visibility derived from light extinction that is designed so that incremental changes in the haze index correspond to uniform incremental changes in visual perception, across the entire range of conditions from pristine to highly impaired. The haze index, in units of deciviews (dv), is calculated directly from the total light extinction. That is, deciviews are related to extinction but scaled in such a way that it is perceptually correct. See, [Visibility Terminology](https://www.fs.fed.us/air/visibilityTerminology.htm) by the U.S. Forest Service.

The Haze Index, in deciviews (dv), is given by:

H = 10 \cdot \ln{\left(\frac{0.0195 n + 10}{10}\right)}

where the particle count per deciliter of particles greater than 0.3 \mu \text m is n.

[**Visual Range (Km)**](https://map.purpleair.com/1/mVR%7C1.2/): Often referred to as visibility, this field selection displays the visual range; the distance from the observer that a large dark object (e.g. a mountain top or large building) just disappears from view.

The visual range, in kilometers (km), is given by:

d = \frac{3900}{0.0195 n + 10}

where the particle count per deciliter of particles greater than 0.3 \mu \text m is n.

[**Visual Range (Miles)**](https://map.purpleair.com/1/mVRM%7C1.2/): Often referred to as visibility, this field selection displays the visual range; the distance from the observer that a large dark object (e.g. a mountain top or large building) just disappears from view.

The visual range, in miles (mi), is given by:

d = \frac{2423}{0.0195 n + 10}

where the particle count per deciliter of particles greater than 0.3 \mu \text m is n.

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## Learn More

[Air Quality Index](https://community.purpleair.com/t/air-quality-index-aqi/111)  
[PurpleAir Map Guide](https://community.purpleair.com/t/purpleair-map-guide/90)  
[Which AQI Data Layer to Choose](https://community.purpleair.com/t/which-aqi-data-layer-to-choose/5202)