# Authoring a Lambda
Spatial lambdas are typically composed of three main components:
**1. Input Definition**
Specify the dataset(s) and region of interest (bounding box or selection) to process.
**2. Compute Function**
Write code that iterates through voxels and applies your logic. For example, summing the ore\_grade property forvoxels above a grade threshold.
**3. Output**
Return a summary value (e.g., total\_volume) or create a new dataset (e.g., filtered voxels). Lambdas can alsoattach files or emit logs during execution.
**Sample Python Lambda**
Here's a basic example that sums the volume of high-grade voxels:
```python
def lambda_handler (context, voxel_reader, voxel_writer):
total_volume = 0.0
for voxel in voxel_reader:
if voxel.properties.get('grade',0.0) >= 0.5:
total_volume += voxel.size
return {'total_volume': total_volume}
```
**Code Explanation**
voxel\_reader**: **Provides voxel objects with property dictionaries and geometry
voxel.properties.get('grade', 0.0)**: **Safely retrieves the grade property with a default valueof 0.0
voxel.size**: **Represents the volume of a voxel (e.g., 1 m³)
**Return value: **Dictionary with the computed total volume that will appear in reports