Question

Finding Locations: What city is farthest from a coal deposit?

Answer 1

I don’t have your map or data, so I can’t pick a specific city. But here’s exactly how to find which city is farthest from any coal deposit, with short worked examples you can run depending on your tools.

General approach
- For each city, compute the distance to the nearest coal deposit (i.e., the minimum distance from that city to any deposit).
- Pick the city with the maximum of those “nearest distances.”

Important notes
- Use an appropriate projected coordinate reference system (CRS) for accurate distance calculations (e.g., UTM or another local metric CRS). If your data are in lat/long, either reproject to a metric CRS or use great-circle distance methods.
- If you have many features, use spatial indexes for performance.

Examples

1) Python (GeoPandas)
- Assumes city and deposit layers as GeoDataFrames with a geometry column.

```python
import geopandas as gpd

cities = gpd.read_file("cities.shp")
deposits = gpd.read_file("coal_deposits.shp")

# Reproject to a metric CRS if currently EPSG:4326
if cities.crs.to_string() == "EPSG:4326":
metric_crs = "EPSG:3857" # or better, a local UTM projection
cities = cities.to_crs(metric_crs)
deposits = deposits.to_crs(metric_crs)

# Create a single geometry of all deposits (fast nearest-distance calc)
deposits_union = deposits.unary_union

# Compute distance (in map units, e.g., meters) to nearest deposit for each city
cities["dist_to_deposit"] = cities.geometry.apply(lambda g: g.distance(deposits_union))

# City farthest from any deposit
farthest = cities.loc[cities["dist_to_deposit"].idxmax()]
print(farthest["city_name"], farthest["dist_to_deposit"])
```

2) PostGIS (SQL)
- Using geography for great-circle meters, or geometry in a projected CRS.

```sql
-- Using geography for lat/lon coordinates (returns meters)
SELECT c.id, c.name,
MIN(ST_Distance(c.geom::geography, d.geom::geography)) AS min_dist_m
FROM cities c
JOIN coal_deposits d ON TRUE
GROUP BY c.id, c.name
ORDER BY min_dist_m DESC
LIMIT 1;
```

3) QGIS (GUI)
- Use “Distance to nearest hub” (Vector > Analysis Tools > Distance to nearest hub) or the NNJoin plugin.
- Input cities as “sources” and coal deposits as “hubs.” Output adds distance; sort to find the max.

4) If your data are CSV lat/long (Haversine)
- Compute great-circle distances from each city to every deposit with haversine formula, take min per city, then maximum across cities. This can be done in Python with the haversine package or in Excel with the haversine formula.

If you want, upload your city and deposit data (or tell me formats: shapefile, GeoJSON, CSV, PostGIS) and I’ll run the exact command/code and tell you which city is farthest.