Aspect Analysis for India
Which way does this land face the sun? Get the dominant compass direction for any plot in India, computed from NASA's 30m elevation data.
What is aspect, and why does the direction of a slope matter?
Aspect is the compass direction a slope faces — north, north-east, east, south-east, south, south-west, west, or north-west. In India, this direction decides how much sunlight a plot receives across the year, which in turn affects solar yield, cooling load, crop viability, and even the resale appeal of hill-station property.
Why aspect matters more in India than people think
India sits entirely north of the equator. The sun is south of directly overhead for most of the year — much more so in winter, less so in summer. This means a south-facing slope in India gets significantly more direct sun across the year than a north-facing slope of the same gradient. The difference is not subtle: a south-facing roof in India receives roughly 20–35% more annual solar radiation than a north-facing roof, depending on latitude and slope steepness.
This single fact drives a long list of practical decisions — and yet aspect is one of the parameters buyers almost never check before purchase. Brokers and sellers rarely mention it. By the time the building is up and the solar panels are paid for, the aspect choice has been locked in for the life of the property.
The eight compass directions and what each one means
North (337.5°–22.5°) — Poor. Least direct sun in India. North-facing slopes are in shadow for much of the day. Cooling loads in summer are not necessarily lower (the surroundings still heat up), but lighting and rooftop solar suffer. Best suited to shade-tolerant horticulture: cardamom, coffee, pepper. Most of the northern face of the Western Ghats and the southern Himalayan foothills falls here.
North-East (22.5°–67.5°) — Poor. Gets morning sun only, loses it by mid-day. Suitable for properties where morning light is the priority and afternoon sun is unwanted. Common in lower Himalayan villages where east-facing courtyards are traditional — the morning sun is a feature, the afternoon shade is welcome in summer.
East (67.5°–112.5°) — Moderate. Strong morning sun, no afternoon sun. Good for residential layouts where waking-up natural light matters and the structure is shaded from harsh afternoon heat. Vastu traditions favour east-facing entrances for this reason. Plots facing east in coastal Andhra Pradesh and Odisha enjoy strong morning light off the Bay of Bengal.
South-East (112.5°–157.5°) — Good. Strong morning sun extending well into the day. Excellent solar exposure with the morning-bias most Indian climates prefer. Most premium hill-station villas in Coorg, Munnar, and the Nilgiris orient bedrooms and verandas south-east — sun and view both.
South (157.5°–202.5°) — Good (optimal). The best aspect for India. Direct sun for the maximum hours per day, year-round. Highest annual solar radiation for rooftop solar. Best winter passive heating. Widest crop calendar. South-facing terraced slopes in the Konkan are India’s most productive paddy and horticulture land for this reason.
South-West (202.5°–247.5°) — Good. Strong afternoon sun, with sun continuing well into the evening in summer. Excellent for solar yield. Can mean higher cooling load in summer afternoons — passive shading design matters here. Many Mumbai high-rises along the Western Express Highway are south-west facing and benefit from sea breezes plus afternoon sun.
West (247.5°–292.5°) — Moderate. Afternoon sun only. Hot west walls are a known cooling-cost issue in tropical India — west-facing bedrooms in Hyderabad, Chennai, and Vijayawada can be 4–6°C warmer than east-facing rooms in summer afternoons. Good for solar if the panel array is angled correctly, but the room layout needs careful design.
North-West (292.5°–337.5°) — Poor. Limited sun, mostly late afternoon. Combines the disadvantages of north (low sun angle) and west (hot afternoon walls). Least preferred orientation for residential building in most of India.
How aspect affects rooftop solar yield
Solar yield is the most quantified benefit of correct aspect. A rooftop solar array on a south-facing slope in Hyderabad will produce roughly 25–30% more annual energy than the same array on a north-facing slope at the same latitude. For a 5 kW residential system generating ~₹75,000 of electricity per year, that is ₹18,000–22,000 of difference every year, for the 25-year life of the system.
Why measured aspect beats “looks south to me”
The eye is poor at compass direction, especially after a slow walk-around with a broker pointing things out. Measured aspect from satellite-derived elevation data is the only honest baseline — it sees the underlying terrain regardless of how a sales pitch describes the view. For high-value plots in hill stations, premium farmhouses, and any property where rooftop solar is part of the plan, aspect should be a documented input, not a guess.
What does the aspect direction mean?
The result card shows the dominant compass direction your plot faces, plus a verdict from Good (south, south-east, south-west) to Poor (north, north-east, north-west). Here is how to interpret each one.
How the analysis works
Three steps. Under one second. No setup.
You mark the plot
Draw the exact boundary on the map, drop a pin at the centre, or paste an address. Works for plots from 1 cent to 100 acres anywhere in India.
We read NASA's 30m elevation
Your plot is overlaid on NASADEM — NASA’s void-filled 30m elevation grid from the SRTM 2000 shuttle mission. We extract every elevation pixel inside your boundary.
You see the dominant direction
We compute the elevation gradient, derive aspect per pixel using atan2, and return the dominant 8-direction compass bearing — plus a sun-exposure verdict.
Methodology and data sources
We use NASA elevation data and compute aspect on the fly. No pre-computed aspect rasters, no proprietary models.
Where the data comes from
The single source is NASADEM HGT v001 — NASA’s reprocessed, void-filled version of the SRTM 2000 shuttle radar elevation data. Resolution is 1 arc-second, roughly 30 metres per pixel on the ground. Aspect is derived from the elevation gradient in the same pass as slope.
How we compute aspect
Aspect is derived on the fly per request from the same elevation window as slope. The steps:
- Read the elevation window covering your plot from
elevation.tif(4.9 GB India-wide int16+ZSTD COG). - Compute physical pixel size in metres, latitude-corrected for India’s latitude.
- Compute the elevation gradient: dy_south, dx_east = np.gradient(elevation_array, y_m, x_m).
- Aspect per pixel: atan2(dx_east, -dy_south) % 360 — compass convention where 0° = North, 90° = East, 180° = South, 270° = West.
- Dominant aspect: circular mean of valid pixel aspects, mapped to the 8-direction compass.
- Flat-terrain exception: if mean slope is below 1°, aspect is undefined — we return “Flat Terrain” instead of a direction.
Coverage and limitations
- Pan-India coverage. 438 NASADEM tiles cover 8–38°N, 68–98°E — all of India and surrounding territories.
- Flat terrain. Aspect is meaningless when the ground is essentially level. We flag this explicitly rather than returning a misleading direction.
- Vintage. NASADEM is based on SRTM 2000 imagery. Recent terracing or earthwork that changed the local terrain face is not in the data.