diff --git a/internal/landscape/compute.go b/internal/landscape/compute.go
new file mode 100644
index 0000000..4bc0e2f
--- /dev/null
+++ b/internal/landscape/compute.go
@@ -0,0 +1,167 @@
+package landscape
+
+import (
+	"context"
+	"fmt"
+	"path/filepath"
+	"runtime"
+	"sync"
+
+	"gis/internal/raster"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// Compute runs one node over its input rasters. See the package doc for the
+// concurrency model: windows are processed by a worker pool; each worker owns
+// its own Reader handles (GDAL datasets are not goroutine-safe) and writes are
+// serialised per output. Window order does not affect the result.
+func Compute(ctx context.Context, rio raster.IO, node Node, inputs map[string]string, outDir string, p Params) (map[string]string, error) {
+	p = p.WithDefaults()
+	paths := make([]string, len(node.Inputs))
+	for i, g := range node.Inputs {
+		path, ok := inputs[g]
+		if !ok || path == "" {
+			return nil, fmt.Errorf("node %s (%s): missing input %q", node.Code, node.Name, g)
+		}
+		paths[i] = path
+	}
+
+	// Validate grids with one set of handles before creating anything.
+	grid, err := checkGrids(ctx, rio, node, paths)
+	if err != nil {
+		return nil, err
+	}
+
+	outPaths := make(map[string]string, len(node.Outputs))
+	writers := make([]raster.Writer, len(node.Outputs))
+	for j, g := range node.Outputs {
+		path := filepath.Join(outDir, g+".tif")
+		w, err := rio.Create(ctx, path, grid, raster.DefaultWriterOptions())
+		if err != nil {
+			closeWriters(writers[:j])
+			return nil, fmt.Errorf("node %s: create output %s: %w", node.Code, g, err)
+		}
+		writers[j] = w
+		outPaths[g] = path
+	}
+
+	windows := raster.Windows(grid.Width, grid.Height, p.WindowSize)
+	jobs := make(chan raster.Window)
+	var writeMu sync.Mutex
+	eg, gctx := errgroup.WithContext(ctx)
+	workers := min(runtime.GOMAXPROCS(0), len(windows))
+	for w := 0; w < workers; w++ {
+		eg.Go(func() error {
+			readers, err := openAll(gctx, rio, paths)
+			if err != nil {
+				return err
+			}
+			defer closeReaders(readers)
+			size := p.WindowSize * p.WindowSize
+			in := make([][]float64, len(paths))
+			for i := range in {
+				in[i] = make([]float64, size)
+			}
+			out := make([][]int16, len(writers))
+			for j := range out {
+				out[j] = make([]int16, size)
+			}
+			for win := range jobs {
+				n := win.Width * win.Height
+				inView := make([][]float64, len(in))
+				for i, r := range readers {
+					if err := r.ReadFloat64(win, in[i][:n]); err != nil {
+						return fmt.Errorf("node %s: read %s window %+v: %w", node.Code, node.Inputs[i], win, err)
+					}
+					inView[i] = in[i][:n]
+				}
+				outView := make([][]int16, len(out))
+				for j := range out {
+					outView[j] = out[j][:n]
+				}
+				node.Kernel(inView, outView, p)
+				writeMu.Lock()
+				for j, wr := range writers {
+					if err := wr.WriteInt16(win, outView[j]); err != nil {
+						writeMu.Unlock()
+						return fmt.Errorf("node %s: write %s window %+v: %w", node.Code, node.Outputs[j], win, err)
+					}
+				}
+				writeMu.Unlock()
+			}
+			return nil
+		})
+	}
+	eg.Go(func() error {
+		defer close(jobs)
+		for _, win := range windows {
+			select {
+			case jobs <- win:
+			case <-gctx.Done():
+				return gctx.Err()
+			}
+		}
+		return nil
+	})
+	runErr := eg.Wait()
+	if err := closeWriters(writers); err != nil && runErr == nil {
+		runErr = err
+	}
+	if runErr != nil {
+		return nil, runErr
+	}
+	return outPaths, nil
+}
+
+// checkGrids opens every input once, verifies all grids match the first, and
+// returns that grid.
+func checkGrids(ctx context.Context, rio raster.IO, node Node, paths []string) (raster.Grid, error) {
+	readers, err := openAll(ctx, rio, paths)
+	if err != nil {
+		return raster.Grid{}, err
+	}
+	defer closeReaders(readers)
+	ref := readers[0].Grid()
+	for i := 1; i < len(readers); i++ {
+		if g := readers[i].Grid(); !rio.SameGrid(ref, g) {
+			return raster.Grid{}, fmt.Errorf("node %s: input %s grid (%dx%d, %v) differs from %s (%dx%d, %v); inputs must be aligned",
+				node.Code, node.Inputs[i], g.Width, g.Height, g.GeoTransform, node.Inputs[0], ref.Width, ref.Height, ref.GeoTransform)
+		}
+	}
+	return ref, nil
+}
+
+func openAll(ctx context.Context, rio raster.IO, paths []string) ([]raster.Reader, error) {
+	readers := make([]raster.Reader, 0, len(paths))
+	for _, p := range paths {
+		r, err := rio.Open(ctx, p)
+		if err != nil {
+			closeReaders(readers)
+			return nil, err
+		}
+		readers = append(readers, r)
+	}
+	return readers, nil
+}
+
+func closeReaders(rs []raster.Reader) {
+	for _, r := range rs {
+		if r != nil {
+			_ = r.Close()
+		}
+	}
+}
+
+func closeWriters(ws []raster.Writer) error {
+	var first error
+	for _, w := range ws {
+		if w == nil {
+			continue
+		}
+		if err := w.Close(); err != nil && first == nil {
+			first = err
+		}
+	}
+	return first
+}
diff --git a/internal/landscape/compute_test.go b/internal/landscape/compute_test.go
new file mode 100644
index 0000000..9f39ae4
--- /dev/null
+++ b/internal/landscape/compute_test.go
@@ -0,0 +1,101 @@
+package landscape
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+
+	"gis/internal/raster"
+)
+
+func grid(w, h int) raster.Grid {
+	return raster.Grid{Width: w, Height: h, GeoTransform: [6]float64{0, 30, 0, 0, 0, -30}, ProjectionWKT: "EPSG:32642"}
+}
+
+func constRaster(w, h int, v float64) []float64 {
+	d := make([]float64, w*h)
+	for i := range d {
+		d[i] = v
+	}
+	return d
+}
+
+func TestCompute_E_TilesWindowsAndWritesEveryPixel(t *testing.T) {
+	fio := newFakeIO()
+	g := grid(10, 7)
+	z := constRaster(10, 7, 2)
+	u := constRaster(10, 7, 4)
+	z[0] = -9999 // pixel 0 invalid
+	fio.put("z.tif", g, z)
+	fio.put("u.tif", g, u)
+	node, _ := NodeByCode("10")
+	p := DefaultParams()
+	p.WindowSize = 4 // forces partial windows (10x7 with 4x4 tiles)
+	out, err := Compute(context.Background(), fio, node, map[string]string{OutZIntegrated: "z.tif", OutUIntegrated: "u.tif"}, "/out", p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := out[OutE]
+	if path != filepath.Join("/out", OutE+".tif") {
+		t.Fatalf("unexpected output path %q", path)
+	}
+	res := fio.files[path]
+	if res.grid != g {
+		t.Fatal("output grid must copy the first input's grid")
+	}
+	for i, v := range res.data {
+		want := 4.0
+		if i == 0 {
+			want = -9999
+		}
+		if v != want {
+			t.Fatalf("pixel %d = %v want %v", i, v, want)
+		}
+	}
+}
+
+func TestCompute_FailsOnGridMismatch(t *testing.T) {
+	fio := newFakeIO()
+	fio.put("z.tif", grid(10, 7), constRaster(10, 7, 2))
+	fio.put("u.tif", grid(9, 7), constRaster(9, 7, 4))
+	node, _ := NodeByCode("10")
+	_, err := Compute(context.Background(), fio, node, map[string]string{OutZIntegrated: "z.tif", OutUIntegrated: "u.tif"}, "/out", DefaultParams())
+	if err == nil {
+		t.Fatal("expected grid mismatch error")
+	}
+	if _, created := fio.files[filepath.Join("/out", OutE+".tif")]; created {
+		t.Fatal("no output must be created on mismatch")
+	}
+}
+
+func TestCompute_FailsOnMissingInput(t *testing.T) {
+	fio := newFakeIO()
+	fio.put("z.tif", grid(2, 2), constRaster(2, 2, 2))
+	node, _ := NodeByCode("10")
+	if _, err := Compute(context.Background(), fio, node, map[string]string{OutZIntegrated: "z.tif"}, "/out", DefaultParams()); err == nil {
+		t.Fatal("expected error for missing input group")
+	}
+}
+
+func TestCompute_MultiOutputNode(t *testing.T) {
+	fio := newFakeIO()
+	g := grid(3, 1)
+	paths := map[string]string{}
+	for i, s := range []string{SlotPIrrigation, SlotPSnow, SlotPCrop, SlotPPasture, SlotPTourism} {
+		paths[s] = s + ".tif"
+		fio.put(paths[s], g, constRaster(3, 1, float64(i+1)))
+	}
+	paths[OutE] = "e.tif"
+	fio.put("e.tif", g, constRaster(3, 1, 3))
+	node, _ := NodeByCode("20")
+	out, err := Compute(context.Background(), fio, node, paths, "/o", DefaultParams())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(out) != 5 {
+		t.Fatalf("want 5 outputs, got %d", len(out))
+	}
+	if fio.files[out[OutCTourism]].data[0] != 3 || fio.files[out[OutCIrrigation]].data[0] != 1 {
+		t.Fatal("min(P, E) not applied per output")
+	}
+}
diff --git a/internal/landscape/fakeio_test.go b/internal/landscape/fakeio_test.go
new file mode 100644
index 0000000..7aca385
--- /dev/null
+++ b/internal/landscape/fakeio_test.go
@@ -0,0 +1,75 @@
+package landscape
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"gis/internal/raster"
+)
+
+// fakeIO keeps rasters in memory keyed by path.
+type fakeIO struct {
+	mu    sync.Mutex
+	files map[string]*fakeRaster
+}
+
+type fakeRaster struct {
+	grid raster.Grid
+	data []float64 // row-major
+}
+
+func newFakeIO() *fakeIO { return &fakeIO{files: map[string]*fakeRaster{}} }
+
+func (f *fakeIO) put(path string, g raster.Grid, data []float64) {
+	f.files[path] = &fakeRaster{grid: g, data: data}
+}
+
+type fakeReader struct{ r *fakeRaster }
+
+func (r *fakeReader) Grid() raster.Grid       { return r.r.grid }
+func (r *fakeReader) NoData() (float64, bool) { return -9999, true }
+func (r *fakeReader) Close() error            { return nil }
+func (r *fakeReader) ReadFloat64(w raster.Window, dst []float64) error {
+	for y := 0; y < w.Height; y++ {
+		copy(dst[y*w.Width:(y+1)*w.Width], r.r.data[(w.Y+y)*r.r.grid.Width+w.X:(w.Y+y)*r.r.grid.Width+w.X+w.Width])
+	}
+	return nil
+}
+
+type fakeWriter struct {
+	f *fakeIO
+	r *fakeRaster
+}
+
+func (w *fakeWriter) WriteInt16(win raster.Window, src []int16) error {
+	w.f.mu.Lock()
+	defer w.f.mu.Unlock()
+	for y := 0; y < win.Height; y++ {
+		for x := 0; x < win.Width; x++ {
+			w.r.data[(win.Y+y)*w.r.grid.Width+win.X+x] = float64(src[y*win.Width+x])
+		}
+	}
+	return nil
+}
+func (w *fakeWriter) Close() error { return nil }
+
+func (f *fakeIO) Open(_ context.Context, path string) (raster.Reader, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	r, ok := f.files[path]
+	if !ok {
+		return nil, fmt.Errorf("fake: %s not found", path)
+	}
+	return &fakeReader{r: r}, nil
+}
+
+func (f *fakeIO) Create(_ context.Context, path string, g raster.Grid, _ raster.WriterOptions) (raster.Writer, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	r := &fakeRaster{grid: g, data: make([]float64, g.Width*g.Height)}
+	f.files[path] = r
+	return &fakeWriter{f: f, r: r}, nil
+}
+
+func (f *fakeIO) SameGrid(a, b raster.Grid) bool { return a == b }