In geospatial analytics, a spectral index is a **calculated numerical value** derived from the measurements of electromagnetic radiation across specific wavelengths in the electromagnetic spectrum, often captured by remote sensing instruments. In simpler terms, you can use a spectral index to derive valuable information by the **ratio of broadband spectral bands** or by **applying mathematical operations on available bands**. Aurora offers you with two types of indices:

You can use the preset indices, which are pretty common in geospatial studies. A few examples are **NDVI, NDWI, VARI, etc**. All these presets have different uses and outputs. One of the commonly used preset indices, the **Normalized Difference Vegetation Index (NDVI)**, measures how green and healthy the vegetation is on the Earth’s surface. It is calculated by comparing the amount of near-infrared light (which plants reflect strongly) and red light (which plants absorb) that is reflected by the land cover. NDVI values range from -1 to +1, where higher values indicate more green and dense vegetation and lower values indicate less or no vegetation. Refer to the [List of Available Preset Indices here](/documentation/analytics_tools/visualizations/Indices/available_indices).

You can create **your own custom indices** for specific use. Aurora gives you the freedom to experiment or customize how you use the spectral data. You can **create any formulations of the bands** as per your requirement and visualize the same while tempering with Rescale value at the same time. Follow the below steps to create a custom index. > **Note**: The custom indices created will be created on the organization level i.e. anyone in your organization can access the index created and saved by you in your AOI.