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Many users understand the calculation logic clearly when they first work with expressions, but run into problems as soon as they need to write the actual formula.

• Band numbers are easy to mistype.
• Nested where(...) expressions make it easy to miss a parenthesis.
• Once conditions become complex, it is hard to tell whether the logic has been reversed.
• The desired result may be "population density", "risk level", or "elevation zone", but the business rule is clearer in your head than the formula syntax.

The Raster Calculator and Field Calculator in iXGIS now support AI-assisted formula writing. In practical terms, you can describe the requirement in plain language first, then let AI turn it into an expression that can run in the current window.

What Is Hillshade?​

Hillshade is a common terrain visualization technique in geographic information systems (GIS). It uses a digital elevation model (DEM) to simulate the light and shadow produced by sunlight over terrain, making elevation changes easier to see.

Core Principle​

Hillshade applies a simplified lighting model to a DEM. For each pixel, the system estimates the local surface orientation from surrounding elevation changes, determines whether the surface faces toward or away from the light source, and then calculates brightness.

Terrain / elevation data describes the elevation form of the Earth's surface. It is usually expressed in meters together with horizontal coordinates, such as longitude/latitude or projected coordinates.

Concepts

• DEM (Digital Elevation Model): a general raster elevation model; depending on context, it may or may not distinguish terrain from surface objects.
• DTM (Digital Terrain Model): bare-earth elevation, with tree canopy and buildings removed.
• DSM (Digital Surface Model): surface elevation, including the highest surfaces such as tree canopy and buildings.

Data forms and formats

• Raster: the most common form, including GeoTIFF, Cloud-Optimized GeoTIFF, and BIL; pixel value = elevation.
• Point cloud: LAS/LAZ data from LiDAR or photogrammetry; can be used to derive DSM/DTM.
• Contours / TIN: vector contours or triangulated irregular networks for cartography or local modeling.

Typical sources

• Satellite / radar: SRTM, NASADEM, ASTER GDEM, ALOS AW3D, Copernicus DEM (GLO-30/90), and partly public TanDEM-X.
• Aerial survey / UAV photogrammetry (SfM): generates dense point clouds and DSM/DTM.
• Airborne / terrestrial LiDAR: high accuracy and high resolution, commonly used in urban and engineering applications.
• Bathymetry: GEBCO, EMODnet, and national hydrographic surveys; often merged with land DEMs into integrated land-and-sea terrain products such as ETOPO.

Land cover describes the current natural or artificial cover types on Earth's surface, such as forest, grassland, cropland, water, and glaciers. Land use describes how people use land, reflecting socioeconomic functions such as farming, urban construction, and industry. In short, land cover asks "what is on the surface," while land use asks "how the land is used." The concepts are related but different: the same forest cover may correspond to different land uses, such as protected forest or commercial logging. In real data products, Land Use/Land Cover (LULC) is often combined into one classification system that considers both natural cover and human use. In general, land cover data is used more for environmental analysis and ecological assessment, while land use data is used more for land management and planning.

Note: At the global scale, direct observation of human land use is difficult. Common global "land use" datasets are usually based on remotely sensed land cover maps, with classes that also imply use. For example, "cropland" and "built-up" are both cover types and land-use indicators. The datasets below are therefore mainly global land cover / land use classification products.

Global vector data refers to geographic data that covers the world and represents natural and human features as points, lines, and polygons. Common features include:

• Natural features: coastlines, international boundaries, rivers, lakes, watersheds, marine regions, terrain-derived lines, and more
• Human features: national/provincial/municipal administrative boundaries, settlements/place names, transportation features such as roads, railways, routes, ports, and airports, protected areas, and more

Common formats/coordinate systems: Shapefile, GeoPackage, GeoJSON, GeoParquet, and similar formats. Most datasets are published in WGS84 (EPSG:4326). Scale/detail: detail is usually described by cartographic scale or minimum mapping unit (MMU), for example 1:110M, 1:50M, or 1:10M.

Common authoritative or widely used data sources at a glance

• Natural Earth (NE): global basemap data, including countries, coastlines, rivers, populated places, and more. It is available at 1:110M, 1:50M, and 1:10M, is clean and suitable for cartography, and is released under a public domain license.
• OpenStreetMap (OSM): crowdsourced global roads, buildings, points of interest, and more. It is detailed and updated quickly, but semantics depend on tags such as highway=*, and quality varies by region. Licensed under ODbL.
• GADM: global administrative boundaries down to county/township levels, with large differences by country and rich attributes. The license is relatively conservative, so review the terms carefully for commercial use.
• FAO GAUL / UN-aligned boundaries: administrative boundaries aligned with United Nations conventions, useful for statistics and governance scenarios. Downloads must comply with the usage statement.
• EEZ (Exclusive Economic Zones, VLIZ): global maritime jurisdiction and sea-area boundaries, commonly used in maritime, fisheries, and ocean planning work.
• HydroBASINS / HydroRIVERS (WWF): global hierarchical watersheds and river networks, convenient for hydrological and freshwater ecology analysis.
• GLWD (Global Lakes & Wetlands): global lake and wetland polygon features.
• WDPA / WD-OECM (Protected Planet databases): global protected-area boundaries and attributes, such as national parks and nature reserves. Licensing and usage statements are strict.
• GSHHG: multi-resolution global coastlines, national boundaries, and rivers, suitable for mapping and coastal analysis.