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Kharita Challenges
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A flat grid of teal pixels with an amber diagonal band, a blue polygon outline laid over it, and a small satellite with teal panels above casting a scan swath

Rasters for the vector analyst

Three delivered rasters — a land-cover map, a July Sentinel-2 scene, an elevation model — worked from acceptance to a programme brief: histograms, zonal statistics, band maths, pixel areas, and the projection rule that keeps them honest.

Remote Sensing

Steps
8
Each assumes the one before it
Time
~6 h
At the problems' own estimates
XP
2,150
Before hint costs and speed bonuses
Progress
0/8
Start the pathBegins with Accept the rasters, or send them back

What you will be able to do

Take delivered rasters through acceptance, summarise a categorical and a continuous band correctly, compute zonal statistics across a CRS boundary without resampling the pixels, turn pixel counts into ground area on a geographic grid, and combine three rasters into one defensible table.

The sequence

Each step assumes the one before it.

  1. Up nextAccept the rasters, or send them backUp nextThe checks a data manager runs on delivered rasters before anyone analyses them: extent, nodata, value range, and whether the figures are plausible for the place.intermediateDifficulty: intermediate200 XP~35 min
  2. 2What is Greater London made of?A class histogram on a 10 m land-cover raster: the shares a planning document quotes, and the reason a pixel count is not quite an area.beginnerDifficulty: beginner140 XP~25 min
  3. 3Why a cloud-optimised GeoTIFF is cheap to serveRead a COG's internal structure — tiles, overviews, bytes — and turn it into the numbers a tile server's capacity plan rests on.intermediateDifficulty: intermediate200 XP~30 min
  4. 4Which boroughs have the least tree cover?Zonal statistics on a categorical raster: the share of tree-cover pixels inside each borough polygon, for a tree-planting programme's targeting.intermediateDifficulty: intermediate230 XP~40 min
  5. 5How green was London on 11 July 2025?Compute NDVI from a two-band Sentinel-2 clip, handle nodata and integer types properly, and report the distribution a monitoring programme quotes.intermediateDifficulty: intermediate220 XP~35 min
  6. 6Mean NDVI per borough, across a projection boundaryZonal statistics where the raster is in UTM and the polygons are in WGS 84: reproject the right layer, compute the index per borough, and hand back a map.advancedDifficulty: advanced300 XP~50 min
  7. 7How much of each borough lies below ten metres?Threshold a DEM, count inside polygons, and turn pixels into square kilometres on a geographic grid — a flood-screening figure per borough.intermediateDifficulty: intermediate240 XP~40 min
  8. 8Defend a borough greening shortlistProjectMeasure canopy and summer vegetation on their own grids, then add low-ground context and apply one transparent shortlist rule.advancedDifficulty: advanced620 XP~110 min

Where it leads

Remote Sensing is examined in the Raster Analyst — Associate, which issues the Kharita Certified Raster Analyst (Associate) (KRA-A1). The problems here are the practice; the assessment is the same kind of problem, under time.