diff --git a/metric/doc.go b/metric/doc.go
deleted file mode 100644
index c0b2f5d11..000000000
--- a/metric/doc.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-// Package metric contains a data model and exporter support for metrics.
-package metric // import "go.opencensus.io/metric"
diff --git a/metric/metric.go b/metric/metric.go
deleted file mode 100644
index 74b8e2b52..000000000
--- a/metric/metric.go
+++ /dev/null
@@ -1,55 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package metric
-
-import (
-	"time"
-
-	"go.opencensus.io/resource"
-)
-
-// LabelValue represents the value of a label. A missing value (nil) is distinct
-// from an empty string value.
-type LabelValue *string
-
-// NewLabelValue creates a new non-nil LabelValue that represents the given string.
-func NewLabelValue(val string) LabelValue {
-	return &val
-}
-
-// Descriptor holds metadata about a metric.
-type Descriptor struct {
-	Name        string   // full name of the metric
-	Description string   // human-readable description
-	Unit        Unit     // units for the measure
-	Type        Type     // type of measure
-	LabelKeys   []string // label keys
-}
-
-// Metric represents a quantity measured against a resource with different
-// label value combinations.
-type Metric struct {
-	Descriptor Descriptor         // metric descriptor
-	Resource   *resource.Resource // resource against which this was measured
-	TimeSeries []*TimeSeries      // one time series for each combination of label values
-}
-
-// TimeSeries is a sequence of points associated with a combination of label
-// values.
-type TimeSeries struct {
-	LabelValues []LabelValue // label values, same order as keys in the metric descriptor
-	Points      []Point      // points sequence
-	StartTime   time.Time    // time we started recording this time series
-}
diff --git a/metric/point.go b/metric/point.go
deleted file mode 100644
index 1a433af03..000000000
--- a/metric/point.go
+++ /dev/null
@@ -1,239 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package metric
-
-import (
-	"time"
-
-	"go.opencensus.io/exemplar"
-)
-
-// Point is a single data point of a time series.
-type Point struct {
-	// Time is the point in time that this point represents in a time series.
-	Time time.Time
-	// ValueType is the type of value held in this point.
-	ValueType ValueType
-	// Value is the value of this point. Prefer using ReadValue to switching on
-	// the value type, since new value types might be added.
-	Value interface{}
-}
-
-//go:generate stringer -type ValueType
-
-// ValueType is the type of value held in a point.
-type ValueType int
-
-// Value types. New value types may be added.
-const (
-	ValueTypeFloat64 ValueType = iota
-	ValueTypeInt64
-	ValueTypeDistribution
-	ValueTypeSummary
-)
-
-// NewFloat64Point creates a new Point holding a float64 value.
-func NewFloat64Point(t time.Time, val float64) Point {
-	return Point{
-		ValueType: ValueTypeFloat64,
-		Value:     val,
-		Time:      t,
-	}
-}
-
-// NewInt64Point creates a new Point holding an int64 value.
-func NewInt64Point(t time.Time, val int64) Point {
-	return Point{
-		ValueType: ValueTypeInt64,
-		Value:     val,
-		Time:      t,
-	}
-}
-
-// NewDistributionPoint creates a new Point holding a Distribution value.
-func NewDistributionPoint(t time.Time, val *Distribution) Point {
-	return Point{
-		ValueType: ValueTypeDistribution,
-		Value:     val,
-		Time:      t,
-	}
-}
-
-// NewSummaryPoint creates a new Point holding a Summary value.
-func NewSummaryPoint(t time.Time, val *Summary) Point {
-	return Point{
-		ValueType: ValueTypeSummary,
-		Value:     val,
-		Time:      t,
-	}
-}
-
-// ValueVisitor allows reading the value of a point.
-type ValueVisitor interface {
-	VisitFloat64Value(float64)
-	VisitInt64Value(int64)
-	VisitDistributionValue(*Distribution)
-	VisitSummaryValue(*Summary)
-}
-
-// ReadValue accepts a ValueVisitor and calls the appropriate method with the
-// value of this point.
-// Consumers of Point should use this in preference to switching on the type
-// of the value directly, since new value types may be added.
-func (p Point) ReadValue(vv ValueVisitor) {
-	switch v := p.Value.(type) {
-	case int64:
-		vv.VisitInt64Value(v)
-	case float64:
-		vv.VisitFloat64Value(v)
-	case *Distribution:
-		vv.VisitDistributionValue(v)
-	case *Summary:
-		vv.VisitSummaryValue(v)
-	default:
-		panic("unexpected value type")
-	}
-}
-
-// Distribution contains summary statistics for a population of values. It
-// optionally contains a histogram representing the distribution of those
-// values across a set of buckets.
-type Distribution struct {
-	// Count is the number of values in the population. Must be non-negative. This value
-	// must equal the sum of the values in bucket_counts if a histogram is
-	// provided.
-	Count int64
-	// Sum is the sum of the values in the population. If count is zero then this field
-	// must be zero.
-	Sum float64
-	// SumOfSquaredDeviation is the sum of squared deviations from the mean of the values in the
-	// population. For values x_i this is:
-	//
-	//     Sum[i=1..n]((x_i - mean)^2)
-	//
-	// Knuth, "The Art of Computer Programming", Vol. 2, page 323, 3rd edition
-	// describes Welford's method for accumulating this sum in one pass.
-	//
-	// If count is zero then this field must be zero.
-	SumOfSquaredDeviation float64
-	// BucketOptions describes the bounds of the histogram buckets in this
-	// distribution.
-	//
-	// A Distribution may optionally contain a histogram of the values in the
-	// population.
-	//
-	// If nil, there is no associated histogram.
-	BucketOptions *BucketOptions
-	// Bucket If the distribution does not have a histogram, then omit this field.
-	// If there is a histogram, then the sum of the values in the Bucket counts
-	// must equal the value in the count field of the distribution.
-	Buckets []Bucket
-}
-
-// BucketOptions describes the bounds of the histogram buckets in this
-// distribution.
-type BucketOptions struct {
-	// Bounds specifies a set of buckets with arbitrary upper-bounds.
-	// This defines len(bounds) + 1 (= N) buckets. The boundaries for bucket
-	// index i are:
-	//
-	// [0, Bounds[i]) for i == 0
-	// [Bounds[i-1], Bounds[i]) for 0 < i < N-1
-	// [Bounds[i-1], +infinity) for i == N-1
-	Bounds []float64
-}
-
-// Bucket represents a single bucket (value range) in a distribution.
-type Bucket struct {
-	// Count is the number of values in each bucket of the histogram, as described in
-	// bucket_bounds.
-	Count int64
-	// Exemplar associated with this bucket (if any).
-	Exemplar *exemplar.Exemplar
-}
-
-// Summary is a representation of percentiles.
-type Summary struct {
-	// Count is the cumulative count (if available).
-	Count int64
-	// Sum is the cumulative sum of values  (if available).
-	Sum float64
-	// HasCountAndSum is true if Count and Sum are available.
-	HasCountAndSum bool
-	// Snapshot represents percentiles calculated over an arbitrary time window.
-	// The values in this struct can be reset at arbitrary unknown times, with
-	// the requirement that all of them are reset at the same time.
-	Snapshot Snapshot
-}
-
-// Snapshot represents percentiles over an arbitrary time.
-// The values in this struct can be reset at arbitrary unknown times, with
-// the requirement that all of them are reset at the same time.
-type Snapshot struct {
-	// Count is the number of values in the snapshot. Optional since some systems don't
-	// expose this. Set to 0 if not available.
-	Count int64
-	// Sum is the sum of values in the snapshot. Optional since some systems don't
-	// expose this. If count is 0 then this field must be zero.
-	Sum float64
-	// Percentiles is a map from percentile (range (0-100.0]) to the value of
-	// the percentile.
-	Percentiles map[float64]float64
-}
-
-//go:generate stringer -type Type
-
-// Type is the overall type of metric, including its value type and whether it
-// represents a cumulative total (since the start time) or if it represents a
-// gauge value.
-type Type int
-
-// Metric types.
-const (
-	TypeGaugeInt64 Type = iota
-	TypeGaugeFloat64
-	TypeGaugeDistribution
-	TypeCumulativeInt64
-	TypeCumulativeFloat64
-	TypeCumulativeDistribution
-	TypeSummary
-)
-
-// IsGuage returns true if the metric type represents a gauge-type value.
-func (t Type) IsGuage() bool {
-	switch t {
-	case TypeGaugeInt64, TypeGaugeFloat64, TypeGaugeDistribution:
-		return true
-	default:
-		return false
-	}
-}
-
-// ValueType returns the type of value of the points of metrics of the receiver
-// type.
-func (t Type) ValueType() ValueType {
-	switch t {
-	case TypeGaugeFloat64, TypeCumulativeFloat64:
-		return ValueTypeFloat64
-	case TypeGaugeDistribution, TypeCumulativeDistribution:
-		return ValueTypeDistribution
-	case TypeGaugeInt64, TypeCumulativeInt64:
-		return ValueTypeInt64
-	case TypeSummary:
-		return ValueTypeSummary
-	default:
-		panic("unexpected metric.Type value")
-	}
-}
diff --git a/metric/producer.go b/metric/producer.go
deleted file mode 100644
index 7902324f7..000000000
--- a/metric/producer.go
+++ /dev/null
@@ -1,84 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package metric
-
-import (
-	"sync"
-)
-
-// Producer is a source of metrics.
-type Producer interface {
-	// Read should return the current values of all metrics supported by this
-	// metric provider.
-	// The returned metrics should be unique for each combination of name and
-	// resource.
-	Read() []*Metric
-}
-
-// Registry maintains a set of metric producers for exporting. Most users will
-// rely on the DefaultRegistry.
-type Registry struct {
-	mu      sync.RWMutex
-	sources map[*uintptr]Producer
-	ind     uint64
-}
-
-var _ Producer = (*Registry)(nil)
-
-// NewRegistry creates a new Registry.
-func NewRegistry() *Registry {
-	m := &Registry{
-		sources: make(map[*uintptr]Producer),
-		ind:     0,
-	}
-	return m
-}
-
-// Read returns all the metrics from all the metric produces in this registry.
-func (m *Registry) Read() []*Metric {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	ms := make([]*Metric, 0, len(m.sources))
-	for _, s := range m.sources {
-		ms = append(ms, s.Read()...)
-	}
-	return ms
-}
-
-// AddProducer adds a producer to this registry.
-func (m *Registry) AddProducer(source Producer) (remove func()) {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	if source == m {
-		panic("attempt to add registry to itself")
-	}
-	tok := new(uintptr)
-	m.sources[tok] = source
-	return func() {
-		m.mu.Lock()
-		defer m.mu.Unlock()
-		delete(m.sources, tok)
-	}
-}
-
-var defaultReg = NewRegistry()
-
-// DefaultRegistry returns the default, global metric registry for the current
-// process.
-// Most applications will rely on this registry but libraries should not assume
-// the default registry is used.
-func DefaultRegistry() *Registry {
-	return defaultReg
-}
diff --git a/metric/producer_test.go b/metric/producer_test.go
deleted file mode 100644
index eb7ffe4f0..000000000
--- a/metric/producer_test.go
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package metric
-
-import (
-	"testing"
-)
-
-func TestRegistry_AddProducer(t *testing.T) {
-	r := NewRegistry()
-	m1 := &Metric{
-		Descriptor: Descriptor{
-			Name: "test",
-			Unit: UnitDimensionless,
-		},
-	}
-	remove := r.AddProducer(&constProducer{m1})
-	if got, want := len(r.Read()), 1; got != want {
-		t.Fatal("Expected to read a single metric")
-	}
-	remove()
-	if got, want := len(r.Read()), 0; got != want {
-		t.Fatal("Expected to read no metrics")
-	}
-}
-
-type constProducer []*Metric
-
-func (cp constProducer) Read() []*Metric {
-	return cp
-}
diff --git a/metric/type_string.go b/metric/type_string.go
deleted file mode 100644
index ae5be36b1..000000000
--- a/metric/type_string.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Code generated by "stringer -type Type"; DO NOT EDIT.
-
-package metric
-
-import "strconv"
-
-const _Type_name = "TypeGaugeInt64TypeGaugeFloat64TypeGaugeDistributionTypeCumulativeInt64TypeCumulativeFloat64TypeCumulativeDistributionTypeSummary"
-
-var _Type_index = [...]uint8{0, 14, 30, 51, 70, 91, 117, 128}
-
-func (i Type) String() string {
-	if i < 0 || i >= Type(len(_Type_index)-1) {
-		return "Type(" + strconv.FormatInt(int64(i), 10) + ")"
-	}
-	return _Type_name[_Type_index[i]:_Type_index[i+1]]
-}
diff --git a/metric/unit.go b/metric/unit.go
deleted file mode 100644
index 7372b592b..000000000
--- a/metric/unit.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2018, OpenCensus Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package metric
-
-// Unit is a string encoded according to the case-sensitive abbreviations from the
-// Unified Code for Units of Measure: http://unitsofmeasure.org/ucum.html
-type Unit string
-
-const (
-	UnitDimensionless Unit = "1"
-	UnitBytes         Unit = "By"
-	UnitMilliseconds  Unit = "ms"
-)
diff --git a/metric/valuetype_string.go b/metric/valuetype_string.go
deleted file mode 100644
index 9fa4a3fad..000000000
--- a/metric/valuetype_string.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Code generated by "stringer -type ValueType"; DO NOT EDIT.
-
-package metric
-
-import "strconv"
-
-const _ValueType_name = "ValueTypeFloat64ValueTypeInt64ValueTypeDistributionValueTypeSummary"
-
-var _ValueType_index = [...]uint8{0, 16, 30, 51, 67}
-
-func (i ValueType) String() string {
-	if i < 0 || i >= ValueType(len(_ValueType_index)-1) {
-		return "ValueType(" + strconv.FormatInt(int64(i), 10) + ")"
-	}
-	return _ValueType_name[_ValueType_index[i]:_ValueType_index[i+1]]
-}
diff --git a/tag/map_codec.go b/tag/map_codec.go
index e88e72777..3e998950c 100644
--- a/tag/map_codec.go
+++ b/tag/map_codec.go
@@ -162,9 +162,6 @@ func (eg *encoderGRPC) bytes() []byte {
 // Encode encodes the tag map into a []byte. It is useful to propagate
 // the tag maps on wire in binary format.
 func Encode(m *Map) []byte {
-	if m == nil {
-		return nil
-	}
 	eg := &encoderGRPC{
 		buf: make([]byte, len(m.m)),
 	}