feat: Update README

docs/gis/gis_example_query.md

@@ -0,0 +1,138 @@
+# GIS Example Queries
+## Common PostGIS Queries
+
+This dataset is compatible with PostgreSQL + PostGIS and supports common spatial operations such as point-in-polygon lookup, area calculation, distance measurement, and GeoJSON export.
+
+### Frequently Used Spatial Functions
+
+| Function | Purpose | Common Use Cases |
+|-----------|-----------|------------------|
+| `ST_Contains()` | Checks whether a geometry contains another geometry | Find which province/ward contains a GPS coordinate |
+| `ST_Within()` | Checks whether a geometry is inside another geometry | Reverse lookup of administrative boundaries |
+| `ST_Intersects()` | Checks whether two geometries overlap | Spatial filtering and GIS analysis |
+| `ST_Distance()` | Calculates distance between geometries | Nearest administrative unit search |
+| `ST_Area()` | Calculates polygon area | Area statistics and reporting |
+| `ST_Centroid()` | Returns the center point of a polygon | Display province/ward markers on maps |
+| `ST_AsGeoJSON()` | Converts geometry into GeoJSON | Web map integration (Leaflet, OpenLayers, Mapbox) |
+| `ST_X()` / `ST_Y()` | Extract longitude and latitude from a point | Coordinate export |
+| `ST_Transform()` | Converts geometry between coordinate systems | Accurate area and distance calculations |
+| `ST_Buffer()` | Creates a buffer zone around a geometry | Radius-based spatial search |
+
+---
+
+### Find Province/Ward by GPS Coordinate
+
+Given a longitude and latitude, determine which province contains the point.
+
+```sql
+SELECT *
+FROM gis_wards
+WHERE bbox && ST_SetSRID(
+        ST_Point(106.65735539347402, 10.767883941562623),
+        4326
+      )
+AND ST_Contains(geom, ST_SetSRID(ST_Point(106.65735539347402, 10.767883941562623), 4326));
+```
+
+### Export Boundary as GeoJSON
+
+Convert geometry into GeoJSON for use with web mapping libraries.
+
+```sql
+SELECT
+    ward_code,
+    ST_AsGeoJSON(geom) AS geojson
+FROM gis_wards;
+```
+
+---
+
+### Get Province Center Point
+
+Retrieve the centroid of each province.
+
+```sql
+SELECT
+    province_code,
+    ST_Y(ST_Centroid(geom)) AS latitude,
+    ST_X(ST_Centroid(geom)) AS longitude
+FROM gis_provinces;
+```
+
+---
+
+### Calculate Province Area
+
+Calculate province area in square kilometers.
+
+```sql
+SELECT
+    name,
+    ROUND(
+        ST_Area(
+            ST_Transform(geom, 3857)
+        ) / 1000000,
+        2
+    ) AS area_km2
+FROM province;
+```
+
+---
+
+### Find Provinces Intersecting a Geometry
+
+Find provinces that intersect a given geometry.
+
+```sql
+SELECT
+    name
+FROM province
+WHERE ST_Intersects(
+    geom,
+    :geometry
+);
+```
+
+---
+
+### Calculate Distance to Province Center
+
+Measure the distance between a GPS coordinate and province centroids.
+
+```sql
+SELECT
+    name,
+    ROUND(
+        ST_Distance(
+            ST_Centroid(geom)::geography,
+            ST_SetSRID(
+                ST_Point(106.7009, 10.7769),
+                4326
+            )::geography
+        ) / 1000,
+        2
+    ) AS distance_km
+FROM province;
+```
+
+---
+
+### Find Wards Within a Radius
+
+Find wards within 5 km of a location.
+
+```sql
+SELECT
+    ward_code
+FROM gis_wards
+WHERE ST_Intersects(
+    geom,
+    ST_Buffer(
+        ST_SetSRID(
+            ST_Point(106.7009, 10.7769),
+            4326
+        )::geography,
+        5000
+    )::geometry
+);
+```

docs/gis/gis_readme.md

@@ -387,6 +387,7 @@ For most users of this project, [DBeaver](https://dbeaver.io/) is the recommende
 
 - [PostGIS Documentation](https://postgis.net/documentation/)
 - [MySQL Spatial Data Types](https://dev.mysql.com/doc/refman/8.0/en/spatial-types.html)
+- [MySQL Spatial Analysis Functions](https://dev.mysql.com/doc/refman/8.4/en/spatial-analysis-functions.html)
 - [SQL Server Spatial Data](https://docs.microsoft.com/en-us/sql/relational-databases/spatial/spatial-data-sql-server)
 - [GIS Concepts & Standards](https://en.wikipedia.org/wiki/Geographic_information_system)
 - [WGS 84 Reference System](https://epsg.io/4326)

docs/gis/gis_readme_vi.md

@@ -402,6 +402,7 @@ Sao chép kết quả GeoJSON và dán vào https://geojson.io/ để xem trực
 
 - [Tài liệu PostGIS](https://postgis.net/documentation/)
 - [Kiểu dữ liệu không gian trong MySQL](https://dev.mysql.com/doc/refman/8.0/en/spatial-types.html)
+- [Các hàm không gian trong MySQL](https://dev.mysql.com/doc/refman/8.4/en/spatial-analysis-functions.html)
 - [Dữ liệu không gian trong SQL Server](https://docs.microsoft.com/en-us/sql/relational-databases/spatial/spatial-data-sql-server)
 - [Khái niệm và tiêu chuẩn GIS](https://en.wikipedia.org/wiki/Geographic_information_system)
 - [Hệ quy chiếu WGS 84](https://epsg.io/4326)